All bets are off
Definition 1 of 2
Pro Tip 1/3Uncertain Outcome
Use it when something unexpected could change the expected result. 
They were leading at halftime, but with the star player injured, all bets are off.
Pro Tip 2/3No Guarantees
It implies that guarantees or predictions no longer apply. 
If the weather turns bad, all bets are off for the outdoor concert.
Pro Tip 3/3Context Dependent
Its meaning can depend on the context; not always about actual betting. 
She's always punctual, but during rush hour, all bets are off.