>Does anyone really believe Russia will eventually just surrender and leave?

With internal turmoil, yes. To maintain the lines in Ukraine Russia needs to constantly send in troops and materiel.

Eventually Russia may decide not to do so. And then there is no magic "pause the frontlines" button if they do.

There is plenty of precedent for this in Russian history too. The Russian Revolution collapsed the frontlines in WWI. The Soviet Empire collapsed with the fall of communism and concomitant internal turmoil.

Russian propaganda puts a lot effort into treating Russia as some sort of force of nature that cannot be deterred or reasoned with, that will advance and hold Ukraine at all costs.

It isn't true. They're humans like the rest of us, not a natural, unstoppable force.