“The water has gone over his head.”

He's past the point of no return, so he may as well go all the way.

Heard in the wild

دیگه آب از سرم گذشته، بذار کل حقیقت رو بگم.

I'm in too deep now. I might as well tell the whole truth.

A note

The full proverb adds: once the water is over your head, one reed's depth or a hundred, what's the difference?

More luck and fate

چشمت روز بد نبینه
cheshmet ruz-e bad nabine
“May your eyes never see a bad day.”
The dramatic opening to a tale of disaster: you wouldn't believe what happened next.
کار از کار گذشته
kâr az kâr gozashte
“The job has gone past the job.”
It's too late now; what's done is done.
آسمون به زمین نمیاد
âsemun be zamin nemiâd
“The sky won't fall to the ground.”
It's not the end of the world.
از این ستون به اون ستون فرجه
az in sotun be un sotun faraje
“From this pillar to that pillar, there's relief.”
Buy yourself some time; something may turn up.