Let’s forget about the Oops TPK, but let’s discuss about the time it ended-up greatly, no matter whether the party decided t sacrify their life to save the world (or simply their honour) or that horror game where the PC found-out too late that they’re hopeless and bound to die
This was indeed one of the idea and had w some PC understood it, except that there was no actual traitor just a mind manipulating monsters. So PC having different information (Hallucinations) and knowing a traitor may be among them was enough…
But great session and everyone enjoyed it