I don't think Putin wants to annex Ukraine Soviet Union style. He wants to annex certain pieces of Ukraine that have an awful lot of ethnic Russians in them and then he would like to make Ukraine a puppet state like Belarus to buffer against the West.
I think what Zelinsky is hoping for is that he can draw the war out long enough for a more favorable political environment in the US and Western Europe that provides more material support to push back against Russia and recapture the land it's lost plus a little more. But that's a long time away. I think what he would love is NATO troops in Ukraine but it's not going to happen.
I think what Russia will accept and what will eventually happen is that Russia annexes certain pieces of Ukraine that have an awful lot of ethnic Russians but maybe not quite as many pieces as they would like and that Ukraine stays somewhat neutral between the west and Russia. That second part is really difficult to guarantee in a democracy as most of the people left in Ukraine would almost certainly prefer a closer relationship with the west. Even if a treaty is signed to remain neutral, there will be a lot of political pressure to start aligning with the west.