> Even getting the currently occupied land back is mostly optional.

That's only true in the short term.

If Russia gets out of the war with Ukraine with territory gains, that only serves as incentive to start up again after Russia can regroup. After all, Putin's stated long-term goal is to take the entire country (among others) and restore the USSR.

Of course, taking back the occupied land is also easier said than done, as it would severely weaken Putin domestically to have expended all these resources and lives for nothing. There's no way he can allow that.

Both countries are in a catch-22.