Majoru Oakheart
Adventurer
Most APs are written in such a way that you might as well not use the AP if you go off them. Sure, you have a list of NPCs. Sure, you have a list of locations. However, if the PCs go elsewhere and never come back all of those are likely useless.AP's dont in any way collapse if you go off them.
Also, a large number of these sort of adventure's timelines amount to "when the PCs get here". Take, for instance, the mega adventure Return to the Temple of Elemental Evil. The adventure had the villains attempting to release Tharizdun who would then lay waste to the world and destroy everything. They are doing a ritual to release him. However, the book basically says the ritual can take as long as you want it to. Generally, to build urgency, you should always remind your players that the end of the world could happen any day now to make sure they stay focused on the adventure. However, the idea is to never have the ritual finish...because the PCs will stop it before it does.
If they choose to avoid the adventure, it's perfectly plausible that none of the locations or NPCs described in the adventure will be used at all. It's plausible that the cultists finish their ritual and destroy the world. However, it could take years and might only complete after your entire adventure is complete.
Of course, the adventure pretty much assumes the PCs follow the adventure as written. It is rather linear. If you are playing the adventure, you are pretty much following the tracks exactly as written. If you choose to avoid it, you aren't playing the adventure at all. Meaning you've just wasted the money it costs to buy it.
It's this exact situation that I'm trying to avoid when I "railroad". Sure, it's plausible that the characters might want to become pirates. However, I purchased an AP because I liked the storyline behind it and liked the situations presented in it. I also liked the fact that it made up all the encounters for me so I don't have to put in the work to write my own. I'm lazy. I don't want to do work if I can have someone else do it for me.So say for instance they want to go pirate hunting instead with their ship, or be pirates. Either way. So what? Throw a quick session of pirate based fun at them and then when they come back to claim their rewards or sell their loot you let them know whats happened in the meantime and see if they want to check it out and get back on the AP.
So, I'd likely do everything in my power to prevent them from simply becoming pirates and having to write a new adventure. It would first start with the subtle, hinting that something important is going on and trying to pique their interest in it. If they showed a complete willful disregard for the adventure a couple of times in a row, I'd drop out of character and simply say "Hey, I don't have a pirate adventure planned. I have a cool story here that I'm sure you guys will enjoy if you follow it. However, if you really don't want to play it then I suggest starting over with a new adventure. Maybe one of the other adventures I bought would be more to your liking. If you don't want to play any of the adventures I bought, well then...Anyone else want to DM?"
I don't think of myself as a human holodeck that just serves up anything people ask for. I think of myself as a writer of an interactive story where the plot is written by me but the players get to decide their reactions to the events unfolding.