This insanity will only end when there are no more russians

Ukraine still has deep pools of manpower to tap--they still don't conscript anyone under the age of 27. Running out of soldiers isn't their problem, especially since they very conspicuously switched to a defensive strategy to preserve lives and use drones as a first wave attacker instead of infantry.

Time favours Ukraine. Absent a really shocking reversal in all western aid, they're surviving and advancing. Russia, meanwhile, is incurring deep structural damage to its economy that shows up already as huge labour shortages, high inflation, and high interest rates, along with war-driven destruction of infrastructure. It's steadily marching to a point where economic collapse, internal unrest, or both, demand that Russia withdraw from Ukraine.

Putin either doesn't know or doesn't care that they're not winning, and any replacement for Putin will be Putin*2, so it'll take something societally catastrophic to force the issue, which becomes more likely every day. As long as Ukraine just hangs on, they win by not losing.

Eventually Putin will die. Maybe he'll keep power until his deathbed, maybe there will be a coup and he'll be removed and/or killed. But one way or another, eventually Putin will die. When he does, this insanity can end.

I don't know that it can end from anything short of that.