Putin was so concerned about NATO expanding right to Russia's doorstep that he did an invasion that immediately led to NATO expanding right to Russia's doorstep. Even Putin stopped trying to sell that bullshit months ago, probably because it makes him look like a complete idiot.
If the US abandons Ukraine, you think that's the end of the conflict? Completing an invasion is the easy part. It's occupation that's the hard part. That's when the real brutality begins, and Russia doesn't have nearly enough occupiers to do it properly. There will be at least a decade of even more horrific bloodshed, probably ending in a Russian withdrawal.
Your friend's heart might be in the right place, but they don't know how warfare works.
Believe what you want dude but, like I said, even Putin dropped that nonsense.