Once they run out of military hardware probably. Russian military doctrine has throughout ages been to throw massive amounts of human lives at the enemy, same is true for today. At some point however, without military hardware it will become absurd even for them.

Russians themselves have gotten used to consumer goods etc from the west, but they are mostly too afraid to rise up against or fight for Putin, who has most of modern russian state built around himself. So, no uprising from within probably.

Altogether if not the end of summer, then it's into very scary territory. Famine + energy prices - while Russia being unable to advance in Ukraine because of seasonal changes.