Filoni explicitly stated he believes there’s great opportunity for future Star Wars stories that feature Rebels characters and, of course, adding them to projects outside the Rebels franchise would further ingrain them within the franchise as a whole.
The open-endedness to some character fates of Rebels means that Dave Filoni can re-introduce them into live-action Star Wars shows.
In this case, leaving stories inconclusive could be handy in re-introducing these characters via other shows, and giving other creators an existing story to build on.