Honestly it need not even be his demise. There are any number of countries he could flee to, countries without extradition treaties and willing to look the other way for any rich despot looking for a safe harbor. Some small Middle East dictatorship seems a logical choice. But even China would probably offer him refuge. Even North Korea if he's truly desperate. Hell, if he offered to end the war tomorrow, most Western countries would probably be willing to offer Putin amnesty, as painful as that would be. If the choice is between holding Putin accountable and saving another hundred thousand innocent lives, I'll let Putin go.

What he is truly afraid of is losing power. He can keep his life. He can keep at least a lot of his wealth. The one thing he can't flee the country with is his power.

In the modern world, dictators never need fear their personal survival. International pariah dictators all support each other. There's a reason Trump cozies up to despots. The dictators all realize that any of them could be deposed, and that losing power will result flight or death. They're all paranoid and afraid of losing power and their lives. So they all backstop each other and provide what assistance they can. And what even the poorest dictator can offer is protection from extradition.