He was impeached by their congress. I don't know what the Ukrain constitution allows, but it was not just a mob.
If that wasn't constitutional, then bring him back, arrest him on theft and corruption charges, and imprison him.
After armed mobs had driven away all the members that supported him and were outside the parliament building waiting to see if the remaining members voted "correctly".
Yanukovych getting out of the country was the worst possible situation for Ukraine.