If Ukraine were to surrender territory, they would have to be allowed into NATO, to be secured from repeat attack from Russia.

I do think that's one of the more realistic scenarios expected under Trump, though I'm not sure about it having to rest specifically on NATO and not some other written security guarantees. However, in that scenario, Russia gets to keep its gains and the world returns to business as usual, as we saw after Russia's actions in Moldova, Georgia, Syria, Ukraine in 2014, etc (and that's just the military involvement, not to mention the countless influence and infiltration campaigns, isolated sabotage and killings in Europe, among other things). It could stop Russia from moving forward in Ukraine, but it wouldn't stop Russia from choosing another target as it always has.