I can see Putin remaining in power in some form or another until the 2030s or even the 2040s. This is way off topic, but why didn't Putin just simply invade and take over all of Ukraine yet?
Likely because he can't.
Yes he could likely overrun the Ukraine, but it's more complex than that, it's believed the war have cost 2000 Russian soldiers. That's a significant loss for a such limited intervention in a area dominated by pro-Russians with a reformed and modernised army against a broke country with 1/3 of Russia's population with a army 30 years out of date.
A full invasion would cost significant losses, maybe enough to risk a revolt at home, the sanctions would become much uglier, and Ukraine would likely begin to become supported fully by the west with weapon and money.