Once V, then...
This structure indicates that once the action takes place, a specific consequence or result follows, often carrying a warning or negative connotation, used in formal or literary contexts.
Examples
合意が得られたが最後、計画は進むだろう。
Once the agreement is reached, the plan will proceed.
彼が怒るが最後、誰も近寄れない。
Once he gets angry, nobody can approach him.
契約が結ばれたが最後、異議は認められない。
Once the contract is signed, no objections will be accepted.
Quick check
合意が得られたが最後、計画は進むだろう。 (Once the agreement is ___, the plan will proceed.)