This is asked at least once a week, please do a search before posting.
Developer was called out by Google and was threatened with removal because having two separate apps like that violate Google's ToS.
As for moving licenses, just purchase a new one. LJ has been working hard on converting Sync from reddit to Lemmy. Buying a new license puts food on his table and is a good gesture of thanks for taking the effort. He definitely did not have to build a Lemmy version at all.
Being a slightly different app with a different backend i highly doubt this will happen. Also jldawson put in a lot of work and def deserves compensation.