Since Ashtray is the one who notices Custer and Faye's sketchy whispering in episode seven and picks up a knife in preparation for anything that may go awry, some fans believe he will sacrifice himself in order to protect Fez. It's worth noting that this wouldn't be the first time Ashtray throws himself in harm's way to shield Fez against danger. He killed Mouse in the season two premiere and was about ready to take out Cal when he came to their store acting suspiciously.
One Twitter user guessed that the reason Fez is on the ground in angst in the season finale promo is that he just witnessed Ashtray getting killed or severely injured. They added that Ash dying would give Fez a layered storyline as we head into season three of the show.
Another viewer postulated that Custer might've been wearing a wire, and when Ashtray becomes increasingly suspicious of his actions, he stabs him to avoid any trouble. That's when "the police barge in and shoot Ash in front of Fez," they said.
Obviously, if anything like this happened to Ash, Lexi's play would be the last thing on Fez's mind.