Let's say that Trumpy brokers a ceasefire. Zelensky agrees to cede the territory that Russia controls and occupies, but refuses to recognise it as Russian territory and vows to reunite Ukraine at some point in the future.
What I think will happen in this case, is that once peace breaks out and the fighting stops, a good proportion of the the people living in the occupied territories will try to move to 'Free Ukraine' to the west. The Russians will seal the borders to prevent this westward migration and a new Iron Curtain will descend along what is now the front lines.
The Russian authorities will treat anyone suspected of Ukrainian sympathies harshly as paranoid occupation forces throughout history tend to do, and a guerilla war will commence where partisans/terrorists/freedom fighters* will assassinate Russian officials and troops, and bomb Russian facilities and infrastructure.
The Russians will say Ukraine are funding and arming the partisans/terrorists/freedom fighters* and will send the odd ballistic missile into Kiev as a warning. Ukraine will shoot back and it will all kick off again.
*Take your pick.