Putin and his cronies are rebuilding the Russian Empire. Even if they shy away from the former territories of Finland and the Baltics, due to NATO, if they are given legitimate ownership of the occupied Ukrainian lands, they might well try for the rest. It is unlikely that Ukraine would be permitted to join NATO whilst there is a frozen conflict.
Alternatively, they could look to regain the Caucasus, or renounce the independence of the central Asian 'Stans.