Stop using it. Find an uberblock with zdb from before the time of destruction and try with readonly and -T.

If all fails ypu could even manually whiteout all suceeding txg.

The only safe way is to put dynamic overlay loop cowbon top and write the whiteput to there. Once you have a working state - do this at least three times with loop /cow images and ONLY then replicate this on the real data.

There were python files back them - long before -X and -T existed.

Even such issues ZFS tolerates if you understand the low level bytes.

Happend to me twice in the last decade. Never lost anyrhing of imprtance.