Putin has a significant amount of what I think he wanted. If true, holding it is sufficient.
I think he actually has a little more land than he planned for at the onset. He would probably be open to negotiations to end hostilities, but the other side isn't.
Just speculating based on what I know of Russian strategic interests.
For whatever reason(s) the west is unwilling to accept Russia increasing their territory again, so it seems like we're committed to pushing Russia back to the pre war borders. If Ukraine starts to really run out of people we'll need to decide how committed we are.
On the home front, I wouldn't put a "Wag the Dog" play past an embattled uniparty this coming year. They'll need an inciting incident of some kind to justify it to the normies, but that can be arranged.
I also would not put it past the Ukraine, if they think they are really losing the war or losing Western aid to find some Russian uniforms and a Russian body or two, and stage an "attack" on something NATO cares about.