No sounds like a bend over and take it kind of a deal.
Return all the refugees back to their respective countries. Maybe make exceptions if they are willing to go on the front lines. Give them incentives like for every 10 confirmed kills they will receive citizenship or something that says if you are willing to bleed for us then you have earned our hospitality.
That way Ukraine can repel Russia easier and gain a valuable allies in the future.
Repopulating post conflict is a non issue. Throw some incentives, give out some land and within 10-20 years back to original numbers. (Not that lower population is necessarily a bad thing either). All you are suggesting is diluting a genepool
Their overall population has been slashed by 1/3 to 1/2, but their working age young population demographic has vanished almost entirely.
Someone needs to work the fields and mine the minerals, to keep the greater EU project fed and warm
Once this war is over the EU won't be able to feed migrants into a woodchipper as easily, sure you could try to incentivize that now but it wouldn't be productive for a war being fought by autonomous drones. Getting all the migrants slaughtered, that's one bird one stone. What I'm talking about is letting the EU stay afloat on the backs of a subservient african labor brought unwillingly to work fields in some farflung hellhole just like the good ol years. Two birds, one stone.
But barring anything like my plan, you aren't getting Ukraine back to its original population in the next 50 years