I sort of simplified the narrative for the sake of telling the story as more post was more about my friend's after game lecture than the events of the game itself.

For some more elaboration, the bounty hunters actually showed up during the battle with the sheriff and turned it into a four way brawl between the PCs, the Sheriff and his deputies, the Bounty Hunters, and the Zombie Horde, with the townsfolk caught in the middle. I had it set up to be sort of the big showpiece capstone battle for the campaign.

As it turned out the PCs killed the sheriff, the zombies killed the militia, and the deputies killed the zombies. If, at that point, the players had decided to take any course of action together (sneak away, fight, surrender, negotiate, etc.) the game would have been over and we could have moved on to D&D.

Instead each PC decided to go off on their own crazy plan without communicating or coordinating with me or with one another. As a result we ended up with a TPK and the town overrun by zombies, which in retrospect I think was what the players had been going for all along.

I am still not sure why though.

As I said, the last few session went extremely well and I was considering turning this from a one off adventure into a long term campaign. Up until my friend told me that no one wanted me to come back I thought they were just having an off night and that I was being overly sensitive or misreading their actions as disinterest / distaste in the game.