If Russia had not invaded another country it would not have needed to take land to protect its borders. All you are doing is rationalizing Russian aggression. Is this worth the cost that Russia is paying for all of this?
Russia or China had done something similar in Mexico, WE would have invaded, justifiably so.
If Ukraine had abided by the Minsk Accords, this war wouldn't be occurring.
If and buts were candy and nuts, it would be Christmas all year long. But, none of the ifs or buts change reality -- which is that any annexed territory will remain part of Russia. Nothing will change that.