I don't see any possibility of retaking the Donbas and Crimea without NATO boots on the ground.
We can give Ukraine everything they ask for with the exception of more Ukrainians. And Ukraine will run out of fighting men long before Russia will.
I'm an amateur historian so don't take me at my word. But if I'm Zelensky, I would throw everything I have in my armies for an offensive to seize Crimea. I agree that retaking the Donbas is out of the picture but that's not really necessary. If Putin loses Crimea, there's no way he will be able to spin his way out of that one. Unless he decides to nuke the Ukies to save his @$$.