Why would they want to? If this does escalate enough, it would make more sense for them to redouble the efforts for their offensive - they still have plenty of reserves that haven't entered the fray yet.
And then, if the plan to cut off Crimea succeeds, they could try to negotiate with Russia - on much stronger terms.
And Ukraine has the convenient position of just telling Wagner forces something along the lines of "you're a bunch of war criminals, but anyone observed retreating into Russia isn't going to be pursued" if they want to let the infighting do the maximum amount of damage.
I don't know, when the board changes you look for openings. On the military side, I would use the distraction to extract battlefield gains. On the diplomatic side, maybe Putin is willing to give up more, now, than he (or his successor) will later.
And then, if the plan to cut off Crimea succeeds, they could try to negotiate with Russia - on much stronger terms.