They would then have the option to stay in Ukraine, move to Russia, or move to the US.
Would this end the war in Ukraine?
If someone proposed to the US that all US citizens could get Russian and Spanish citizenship, would the US response be to ignore this; to laugh at this; or to be angry that this was suggested, followed by "oh god send guns, the Russians I can see them! Why won't you help us, you signed a treaty to guarantee our borders that's the only reason we agreed to give up our nukes!"
The Ukraine lost several years ago and has no chance of winning at this point as the death toll on there side is not only larger but more devastating.
The thing you need to worry about is the next step, regaining Georgia's oil reserves.