At the moment, I feel like Russia is going to end up trimming off a corridor of land in the South-East. I don’t think it will end up like Germany, split in half.
I expect that Russia will build a wall or DMZ to protect the corridor but that will probably leave the whole rest of the Russia/Ukraine border open to shoot rockets into, from Luhansk all the way North to Belarus and over West to Poland.
I could easily see that taking on parallels with Palestine/Israel and on-going terror acts - rockets, bombings, sabotage, etc. - from Ukraine in to Russia/Belarus. And to be honest, this might be a fairly effective course for Ukraine. Russia is expending what military it has, trying to take the Ukraine corridor. After they’re done, they’re going to be fairly spent and that’s a long-ass border to try and defend. Israel isn’t going to sell them Iron Dome, the US isn’t going to give them Patriot, etc. There’s liable to be not much to prevent Ukraine from driving over to take Gomel, Kursk, etc. if the West keeps them supplied with new tanks, missile launchers, etc.
If they can get started quickly enough, they might be able take more out of Russia than Russia got out of them because there will probably be a friendlier reception. That said, that friendliness will not be there if Ukraine just sits back and bombs the region for a year before sending troops in. They really sort of need to start going for it ASAP. And probably they would really need to form an alliance between other former Russian states to go for it, since they’re also going to be pretty worn out, during the opening. (Addendum: Probably the best way to do this would be to send in small groups of saboteurs to take over the city government, rather than try to take it militarily. You just bring them in to fortify the city.)
Over the long run, though, due to the inability for Russia to defend their border, I would expect that regular attacks on Russia would result in an escalating return of larger and larger missiles coming back as response.
The US is probably going to want to shut all that down before it starts, however, so I would expect that we’ll be advising Zelensky to take the loss and giving him financial incentives to let it go.
So an alternative path would be that Zelensky smiles, accepts US aid, and starts preparing an assassination team to go in and get Putin. Given that the two nations are pretty similar in complexion, language, and culture and they share a long border, that may be relatively do-able.
One result of all of this that is very likely is a unified block of former Soviet states that is united in getting revenge on Russia. Given that several of those will be NATO, that’s going to prove problematic, so, if Zelensky is working on organizing something like that, I expect that it’s going to happen without warning.