I think the most probable timeframe for Ukraine to have called it quits at Bakhmut was early winter as that was the point in time when casualties on the UA side really started to mount and it also became clear that Russia was going to throw everything it had into the battle. The rest of what I wrote applies to that scenario.  Basically, Ukraine was offensively spent and Russia had plenty of time to move stuff around to be ready for the Summer. If Ukraine ceased fighting at Bakhmut, h