If you talk to a Ukrainian, they will tell you that the war will end when they win the war. I.E. they won’t stop fighting until the Russians are gone.
So if the regions remain under Russian control, the fighting will continue. Given Russia couldn’t conquer Ukraine first time round, it seems unlikely that they will be able to support a sustained campaign against a country that isn’t going to give up, until it’s over. Most likely outcome is that Russia attempts to hold the invaded territory for a period of years and eventually leaves when it becomes untenable for Russian leadership
So if the regions remain under Russian control, the fighting will continue. Given Russia couldn’t conquer Ukraine first time round, it seems unlikely that they will be able to support a sustained campaign against a country that isn’t going to give up, until it’s over. Most likely outcome is that Russia attempts to hold the invaded territory for a period of years and eventually leaves when it becomes untenable for Russian leadership