The Ukrainian army has no chance operating in the open. The Russians have the air power and artillery advantage.
If Ukraine wanted to pull out, they would have had to make the withdrawal in small groups over an extended period of time and probably in the night. And regardless of where they pull out to, they will never be in as good a defensive position as in this place which they fortified for like 8 years. If they really want to make a last stand, the best places would be their largest cities, Kharkov, Dnipro, Kiev, and Odessa. But the end result, unless the Russians tire for some reason, is pretty predictable. By the time the Russians get to those places, they will have the experience of storming Mariupol, and possibly also Zaporizhzhia, and Nikolayev, so it won't go as well as the Ukrainian side will expect it to. After the experience with Mariupol against entrenched infantry, Russia rolled out the BMP-T, as I expected. And it seems to have done pretty well. Seems to have been used in the operation in Popasnaya to great effect.