Putin is 71 years old now, has been the president of Russia in some form for over 25 years. He will die in that seat before the war is over.

Yeah, but that could be in decades. I.e. the west shouldn't merely commit to making Ukraine win, it should commit to make Ukraine win soon. That would obviously entail delivering more and more controversial weapons systems and lifting limits on those, but I don't see much of an downside in that.

Russia won't risk its entire population being wiped out just because Western cruise missiles fired by Ukraine blew up a few military bases in the Russian mainland and maybe the odd ministry in Moscow. At this point Russia likely questions whether it actually could start a nuclear war. The Americans have shown how much intelligence they have and how much more advanced their weaponry is. I.e. if Russia escalates in the direction of nuclear, it may very well be decapitated before any of its missiles leave the ground. So fears that delivering weapons to bomb Russian mainland will lead to world war 3 are overblown. That would require a lot of rich people in Russia being willing to die for nothing.