Ukraine has asked the West for a future economic aid program to help finance Ukraine for at least a decade after the end of the war in Ukraine so that it can maintain an active-duty military of 800,000 personnel to repel any attempt at a second Russian invasion in the future.
As AMK said, it is simply not possible numerically nor will it be possible with an economically exhausted West and a degraded Ukrainian population in a post-war environment. With your population dwindling and your army already struggling to maintain numbers, don't you think it's a little out of the park for this?