The die is cast
Definition 1 of 1
Pro Tip 1/3Historical Origin
Originates from Julius Caesar's crossing of the Rubicon, signaling irreversible commitment. 
She bought the one-way ticket to Barcelona, and the die was cast.
Pro Tip 2/3Dramatic Decisions
Used when a decision has significant consequences and emphasizes the moment's gravity. 
By signing the contract, the die was cast for his future with the company.
Pro Tip 3/3Not Literal
It's metaphorical, not about actual dice. Implies a decisive moment has occurred. 
After the vote, the die was cast for the new school policy.