I think the opposition to the give up Crimea part is that Russia has to be demonstrated to demonstrably lose because of their actions. We need to prove that this empire building attitude is an attitude of ancient history and no longer works.

Rather like how Japan was made to give up territory in China at the end of the second world war.

If they are allowed to keep Crimea then there are some who will say that it's worth the risk because sometimes you're allowed to keep the territory.

I think Russia in general would be much more amenable to giving up Crimea if Putin wasn't around anymore. It's not really the world versus Russia it's the world versus Putin, it's not as if Russia has a democracy.