Can you unweld a diff? Simply – no. Once you've welded your diff, it's a done deal, and if you regret your choice further down the line, your best options will be to swap or replace it.

Is it bad to weld your diff?

Welding the differential will put a large amount of stress on these components and the last thing you want is your left axle crumbling to bits mid corner. Get under there, make sure everything's secure and in good condition. For god sake, weld the differential properly or get someone who knows what they're doing.

How long will a welded diff last?

Playworker's was badly welded and lasted about 6 months before breaking IIRC. We just welded it back up and it's been fine since. Mine was welded properly and has lasted about 18 months so far. We welded a diff for someone on Driftworks and that will never break, it's got so much weld in it it's untrue.