Alexander, that could well be the case today but Putin will bide his time, replenish his coffers and return later. Putin having any slice of Ukraine should be up to the Ukrainians and the West pushing for such a solution for the sake of "returning to as before" would be a gross disservice to Ukraine.
As yet, I don't see it as the U.S. poking the nuclear bear and that needs avoiding. Putin is not without options. After all, he can stop the bloodshed and offer some kind of settlement any time.
We could offer Putin a retirement package of security and he keeping some of his loot. That very unpalatable but practical end to Putin would have to be agreed upon of course-- and by Putin.
Excellent article. Best to you.