But if the wizard used up their lightnings, why would they continue?
Then that becomes like a said,a comparison of information and expectations.
Continue
Pro: Maintain The Element of Surprise
Pro: Guards not at high alert
Con: The Wizard is down 2 lighting bolts
Con: Party is not at full HP
Come back tomorrow
Pro: Wizard has 2 more spells
Pro: Fort is down X bugbears
Con: Guards at high alert
Con: Can't use Secret Entrance
Come back.
Pro:" The party will be at full"
Con:" The party lost the element of surprise. The warlord will send seek and destroy parties. The players will be found and they will be attacked in the early hours of the morning with a dispel magic on the tiny hut (if they made one). They will be attacked by the entire compound and the warlord and his close guards will simply watch the show. The group will definitely TPK and after that, I Will, show them the notes about the adventure and how and why they TPKed so drastically. Most players will agree that it was not that good of an idea."
And this is without me doing the rules I use to enforce 6-8 encounters per day.
Pressing on.
Con:" The party is motivated at full strength. A bit weaker, yes, but that is but one encounter."
Con:" The party misses some key spells. Pressing on will only further their problems and they might be forced to take extra precautions."
Con:" In such a weakened state, the party might miss a key attack and a fleeing foe might ring the alarm."
Pro:" The alarm is not set. Most enemies are not aware of an intrusion and might be unarmored. "
Pro:" Since the secret entrance was so well garded. It might be safe to assume that security is high on entrance but low once inside. Fights will probably be easier and if attrition is a thing for the players, so is it for their foes. Picking them in small groups will make it easier for the PCs. Pressing on, will help validate the theory and if the theory proves to be correct, pressing on is the way to go."
Pro:" Pressing on might also mean that key opponents might be caught alone and without help if the guards have been eliminated along the way. Slowly reducing the number of opponents will allow for easier fights. Fighting the whole keep/compound at the same time is a sure way to die."
And if at some point, the alarm is set, depending on the amount of enemies the players have eliminated will work on their favor. If enough, the warlord might decide to flee. If they bravely made a dent because they were unlucky, they will face pursuit but it might be on their own terms. At this point anything can go. But one fight and off? This is a sure way to get a seek and destroy party going against the players and the fight will not be on their own terms.