Unfortunately, the media associated directly to Ancestry Sources ( Ancestry Docs) or other Ancestry users are theirs. The license you purchase (subscription) allows you to access them and most of them you can download as an image also (to manage and utilize under same license). But the quick access (link) to them via Ancestry is only through said subscription.
As well the media you uploaded to Ancestry will have to be re-associated to the new Environment (RootsMagic).
The future updates to RM may allow users to associate those media items from FTM/Ancestry; but that, we will have to wait on.
In short, you probably will have to re-link all of them to RM if you choose to keep it. Though, others may have more to say.
Harold you have diverted away from my concerns. RM does not sync with Ancestry and it would seem that we don't know when this will be. In the meantime I have returned to Windows 10 and FTM. In future if RM syncs they I nay return as I still have the license.