This is my fear. When an agreement is eventually reached and he gets his token bit of victory land and withdraws his troops, the world will quickly forget and loosen it's grip on Russia's neck. These sanctions and controls need to remain in place as long as the current regime is there. It will be costly to everybody though and I'm not sure the political appetite will remain for long after the war is over.
I personally don't think the sanctions will go away as fast as they would be needed to save the Russian economy in time. Western leaders probably see the sanctions as a way to finally get rid of him and will want to leave them in place to further weaken him domestically.
Either way, the dye has been cast.