All DMs know that the PCs have an innate ability to choose to deal with a situation in a way that is one that you didn't consider. Worse, they'll find the choice is one that you did consider, but decided it was so crazy to do so, they wouldn't go for it.
That happened to me last week.
The PCs are in Xen'drik (in Eberron) on the way to a drow tribe that had adopted the warforged fighter/cleric. On the way, they accidentally travelled into the territory of a Vulkoor worshipping drow tribe. They fought one combat against a group of drow, and that night had encamped next to a river.
They were then attacked in the middle of the night by a group of hill giants (along with some mutated frost giants), who had been led there by a pair of drow, using a stolen 'artifact' as bait.
They fairly quickly eliminated the giants, but then heard dozens upon dozens of drow heading for their location. They ran.
A skill challenge then broke out and the PCs nearly succeeded, but ended up failing. They did however, find themselves in a sacred grove featuring an upthrust giant scorpion claw. They knew via a Religion check that the drow would be unwilling to spill blood on their sacred ground.
They were surrounded by about 200 drow, and a rather tense negotiation occured (another skill challenge), which the PCs succeeded at. They had agreed to basically clear out the giant enclave that had been causing the drow problems. However, knowing that they were dealing with powerful people (the PCs are level 18) the drow wanted the PCs to touch the claw and swear to try to defeat the giants, in order to make sure that the PCs would comply with their side of the agreement (effectivelly an old school Geas).
Suddenly the deal fell apart, two of the PCs refusing. At this point, given that it was close to normal quitting time, I should have just called the session there. But I didn't.
This then escalated to the point that the negotiator ordered the drow to 'kill them'. Now, these guys are powerful, but even 190 minions are going to do a lot of damage (375 points to the Assassin).
This bothered me all the way home and the next morning. I emailed the players asking 'WTF?' thinking that there was some sort of communication problem. There was.
1. PCs will choose death over being 'forced' to do something. Even if they've already agreed to it.
2. It's a good idea to have some idea of what the PC's religions are. The Assassin player (one of the two PCs to refuse the Geas) surprised me by basing his objections on his religion...which had never come up in play before. (admittedly, we had less roleplaying previously than we should, and are now trying to focus more on it, but it was still a surprise).
3. Always have an out, even if it involves something the PCs would be insane if they tried.
I have come up with a solution, but we don't play again until next Friday, so I will leave that for the next post.
My question then is, what have other DMs done that resulted in a TPK? What, if anything, did you do to continue the storyline from there?