I think you are wrong about this,giving in to Putin would have only made
him stronger in his believe Russia is invincible and it would even encourage him more to try to "reestablish the old USSR" like he said he wanted to do.
I strongly believe that now he realizes he has made a very big mistake but being the man he is he will never admit that because it will show weakness and that in itself would be very dangerous to him.
It is also very clear to him that even the thought of entering any NATO members country will mean the end of him and Russia as we know it.
You think support to the Ukraine will dwindle,i think it will not.
The USA is getting rid of an age old enemy for a relatively cheap price,there is a lot more to that but that is for another discussion.
No loss of life for them and no real danger,the threat of nuclear war has always been there.
Europe is also realizing that the Ukraine is in fact fighting their battle.
Russia is more and more isolating itself and slowly their economy is collapsing.
You are saying it is not your war,it is a war against pure evil and the Ukraine is fighting for all the right reasons.
Honest question,if you had a neighbor who wanted a piece of your garden for whatever made up reason,would you give it to him to keep the peace?Roll over and show your weakness in the hope he would stop?The world does not work that way.
Do you see what is going on?