Ya, I thought about this too. Ideally, the regions decide their fate, impartial leaders or agencies confirm the results, and an internationally recognized treaty is made, but I don't think anyone trusts anyone with this task. Plus, who knows if Russia, the US, the EU, or Ukraine will accept the outcome.

The OSCE monitored the civil war in Eastern Ukraine since 2014, and reports state the people have been calling for a treaty or Russian support for years. I'm not sure how they feel about Russia now, but it's god damn injustice nothing was done sooner.

Western reports stated violent attacks on Crimeans (apparently, they are mostly of Russian ancestry) stopped after annexation, and the people are happy with the decision. However, Ukraine isn't thrilled, and with US-backing, I'm not sure they'll accept peace with annexed regions, but maybe all they want is peace. Who knows?