hi Andrew, all bets are off...literally, means all bets are cancelled. отмена заключенных пари all bets are off...figuratively, means the situation has changed and no one knows with any certainty what will happen next. Let's say you are at a horserace and have placed a bet on a horse. Before the race begins the favorite horse breaks a leg. The loudspeakers announce, " Ladies and gentelemen all bets are off! Return you tickets!" The conditions of the race have changed and the bookmakers can no longer calculate the chances of any horse winning, so they have called off the bets. In the context of the movie, the zombies have been created by an experimental virus and there are now so many zombies on earth, hungering for human flesh of course, that it is impossible to predict the outcome. No one knows what will happen! It may mean extinction for the human race... all bets are off!

The idiom definition for 'All bets are off' is that if all bets are off, then agreements that have been made no longer apply.

I googled! "all bets are off" = an expression meaning a situation in which one factor alone can change or cancel out everything. e.x. 'When Janine is around Corey, all bets are off...the poor dude just can't be himself anymore.' the sentence obviously implying that the zombies need ONLY ONE THING, the living. all bets are off - meaning a zombie can survive (I wish they couldn't) only in one thing - the living human being, and nothing else does for them. :)