Yes, but only in two games so far. Once from the polish, and once from the argonese. had an heir marry their princess soon before they were taken over and their king was lost with no heirs and they still had territory, so they went rebel, then over to me.

It is a rare thing but in reality it should be rare, how often is it that the king and all his heirs are lost while still having territory left?

Most anyone wants to keep their king and heirs safe by retraeting them to their last province if they have to in order to stay alive.

Resaon I was able to get their lands, was because they couldnt retreat to the land that I eventually got.