Your post suggests ethnic russians are the only ones that matter. There are no trustworthy numbers since Russia annexed Crimea but before that - meaning less than 10 years ago - ethnic russians were just a minority. There are also Ukrainians, Crim tartars and a wealth of smaller groups.

Options:

1. Russia might have managed to drive off other ethnicities and add more russians,but all of which would have been in the past 10 years, knowing full well it's stolen land.do these people get a say on who owns Crimea? I don't think that's something to reward.

2. Russians are still a minority(and not necessarily all of them might want to be part of Russia...). Then clearly your logic would suggest that Ukraine should retake it or Russia voluntarily should hand it back.