This war either ends eventually or we move back to 'there are clear questions about what is going to happen to the stability of the regime' territory.
And when it ends we... also move back to that.
Probably, anyway. I have no crystal ball and you make a good point; the regime has enjoyed nearly 4 years out of stability out of this, that's a win of some sorts.
I believe falling behind former Sovjet countries economically is a continuous pain point for the Putin regime; but getting overtaken by Polish, Slovenian or Czech former "compatriots" is one thing (those being much closer to Europe), but the same happening with Ukraine (or Belarus) would be a whole other story, and seen as complete failure of the regime domestically.
Preventing that is a worthwile outcome for Putins government by itself.