D&D 5E have fun storming Cragmaw Castle! (LMoP spoilers)

So the ragtag bunch of bumbling misfits that I DM for "attempted" a stealthy approach into Cragmaw Castle, which lasted all of 10 seconds.

Basically they alerted the front half of the castle (rooms 1-7) in fairly short order. However, I tend to play hobgoblins as rather crafty and battle-hardened and they started barking out orders to the goblins, which included telling some goblins to run and alert the rest of the castle.

The party mopped up and took some time searching. While this was happening, I had the hobgoblins release the owlbear, which detected the party as they made their way towards room 12 (the owlbear broke the door down and charged). That's where we ended the last session.

The party is somewhat banged up and they discussed resting before moving forward (they are expecting the castle to have a dungeon where the boss will be). Since the final room is written so that the players interrupt a negotiation for Gundren and the map, I'm trying to decide what to do if the party leaves and rests. The adventure gives details in the event Grol and the doppleganger are alerted but not if the players leave for a significant length of time.

Since the rest of the castle is wiped out, I can't imagine they would stick around. I could have Grol and the remaining enemies take the fight to the players, hoping to take them out while they are weakened.

Grol and doppleganger could flee with Gundren and the map. This would be a huge complication for the players since they are relying on finding Gundren (or the map) to give them the location to Wave Echo Cave.

I also had a couple of more "out-of-the-box" ideas:

1. The pressure of the attack makes the negotiation go sour between Grol and the doppleganger. A fight breaks out and knowing it is outnumbered, the doppleganger flees. Grol stays put and waits for reinforcements? Or leaves with Gundren and makes his way towards Wave Echo Cave? Not sure how to resolve this idea.

2. The optional hobgoblin warband arrives as the players are leaving the castle. This could be bad for the players (hehehe) but it may force them back into the castle to rescue Gundren ASAP and find a way to retreat to safety. As a DM, this sounds fun for me.

Any thoughts would be appreciated!

If you haven't established anything in the fiction about the negotiation for Gundren and the map plus any of the related NPCs, then that can be an event that happens after the PCs rest. This is under the idea that stuff doesn't exist until you describe it in play.

Perhaps when the PCs are on their way back for their second foray into the castle, they notice some shady characters arriving just before them allowing you to telegraph those enemies in advance of running into them later.

I see basically two options as you've outlined: They either flee or stay.

However, if they flee they take Gundren and the map with them, I suppose. Or at least the map.

If Gundren and the map do leave, they'd probably an escort-in-force to ensure the map gets safely to wherever they are taking it. Does this escort exist? (That is, are there enough troops left to have a plausible escort?)

If there isn't and the inhabitants expect a warband to arrive, maybe they move with haste to catch the warband and then either assault Cragmaw or move elsewhere.

If they aren't coming back, what information, if any, would there be left behind as clues to there new location? Can the PCs track the hobgoblins?

The hobgoblins can't go too far as they need to be close enough to find the mine.

If you are really unsure as to the reactions of the principals you can always make up a list of plausible outcomes and dice roll it. Maybe you think they don't trust each other and this assault inflamed that distrust. Maybe there was (or will be) a fight. Perhaps if the PCs move quickly enough instead of encountering a negotiation there is an argument that will come to blows. Maybe there already was a fight (who won?) and the winner fled with the map but left Gundren behind.

The situation: Grol has something the Black Spider wants: Gundren and the map. In the middle of negotiations with the Spider's representative, his base is attacked by adventurers after Gundren. Grol now has two parties wanting what he has, and can attempt to play them off of each other.

What happens next: Grol increases his price to the doppelganger. He can explain it as extra gold needed to replace his dead troops, or as recompense for bringing adventurers down on his head. Maybe the doppelganger doesn't have that much gold on hand, or it needs to get the Spider's approval. While it goes back to the cave, Grol sends emissaries to the adventurers, offering up Gundren for a price. Maybe the price is within their reach, maybe it isn't. Meantime, Grol takes steps to conceal Gundren and the map so he maintains his leverage over both groups. He also sends for reinforcements, though will they arrive in time? Perhaps in the middle of an assault by the adventurers, or an infiltration by the doppelganger? Or perhaps Grol takes the prisoner and retreats to where his reinforcements are - say, a camp of goblins he can intimidate.

Lots of possibilities.

There are a lot of possibilities.
When I ran this, the players made short work of the Hobgoblins and the doppleganger had to think fast.
He locked a badly beaten and unconscious Gundren in a closet and then made himself look like the dwarf. The PCs came in and found "Gundren" and were relieved. But what the doppler didn't know is that two of the PCs had a background that gave them history with Gundren and after a few questions they realized he wasn't the genuine article.

HOWEVER.....

If they had fled without rescuing Gundren or stopping the negotiations I had a few things planned.
1. The doppler got the map and now Gundren is dead. Pure and simple. Actions have consequences, and them leaving him there would have meant he was no longer useful.

2. The doppler got the map and Gundren is now a slave of the hobgoblins. They would have had to find them deeper in the forest. Perhaps a second, much more well guarded location.

3. The doppler takes both the map and Gundren to the Spider. Replace the other brother at the end with Gundren or just have them both there.

I just ran this. The party disguised as Redbrands made their way into the castle to see King Grol. They had already planned out what they were going to tell Grol: that they were here to pick up Gundren and to give Grol 200gp for the dwarf and his possessions from Glasstaff (up to 500gp if they needed to). The party successfully bluffs their way in and is escorted to the back of the castle. Grol made the PCs wait outside because he was in the middle of some business. Listening at the door they overheard the negotiations between Grol and the doppleganger and decided they needed to get in on the discussion.

They push open the door demanding to be part of the negotiation. Grol, happy to have a 3-way to up the price for the map, agreed to let them participate. The debate got tense with the party claiming they represented Glasstaff and the Black Spider and the drow/doppelganger claiming she represented the Black Spider. Both sides started claiming that the other side was a fake representative. The party suggested to Grol that both they and the drow/doppelganger should pay Grol and then let them work it out. Grol thought that was a great idea, but with concern over a possible fight in his castle decided he wanted some back-up and started heading to the door to call for his guards. The Drow moves over toward Gundren and party goes into action drawing their weapons, but the drow wins initiative.

The drow's hidden intent in winning the negotiation is to kill Gundren and destroy the map to prevent anyone else from finding the LMoP (since the Black Spider is already there), so she uses her action to kill Gundren. He is already unconscious and the she autocrits for 2d6+4 plus 6d6 surprise damage, so Gudren is killed by damage exceeding his hitpoints in a single blow when he is already at 0. The party dog piles the drow, the first ones unsuccessfully trying to save Gundren and unsuccessfully trying to grapple, the rest deciding they just want to kill her.

In the next round, the drow disengages and moves over to King Grol's bed and the door to the closet. The doppleganger had previously asked Grol where the map was. Of course Grol didn't reveal the location, but since the doppler can read minds she knew exactly where it was. The party takes another round trying to kill her and manages to take her to about half health.

The drow disengages again, grabs the map from under the bed, walks over to the brazier, drops it in and steps to the nearby arrow slit. The party trying to save the map, grabs the burning map from the flaming brazier and tries to put out the flames. The rest attack the drow and fail to kill her. The doppler shifts into a child halfling, squeezes through the arrow slit and jumps to the ground outside.

The map rolls poorly for its save and is unreadable, the party rolls poorly to track the doppleganger and she escapes. The party leaves the 200gp for Grol to get the rest of Gundren and Sildar's possessions and says "at least we know who the impostor was"

They leave the castle deciding not to fight all the goblins in Cragmaw Castle at one time.

EPILOG

What an exciting encounter. With a bit of bad luck from the PCs and some smooth moves from the doppleganger this became one of the most memorable fights of the adventure so far. They are aware that they will have to face a very cunning and powerful foe in the future and it has added hugely to the tension of the plot. The party now has to find the LMoP without Gundren and the map. Fortunately Reidoth the druid in Thundertree knows how to get there and the party knows that the druid knows every inch of the surrounding land, so they suspect he can help them. This provides an interesting adventure hook for the party to go to Thundertree.

Other thoughts:

Grol's choice to change the original deal with the Black Spider and sell the map was a serious problem for the doppleganger because it was an unexpected complication to an otherwise smooth pick up. The doppleganger isn't listed as carrying any cash and so the doppleganger could only make promises at the bargaining table. This gave the doppleganger a huge disadvantage against the PC's sack of gold.

I had the full map for cragmaw castle built but then the PCS skip the entire thing they just did not go in. They found out Gundren had been moved to wave Echo cave and decided to find it first.

We had to fight the whole castle in waves, and we had the patrol also, but i think we rested before. Otoh we aquired the castle as a base for the charakters.

In the game I ran: When the PCs left the castle and rested, the Black Spider's minion left, taking Gundren with her. By the time the characters came back and found her tracks, she had killed Gundren and escaped.