@benjamineskola
in either case, previous versions remain available.
Correct. Even if the controller of the public #git repo takes it down without warning, the community can still fork the project based on the local copies of the repo that various people have lying around.
It seems to me like the core problem is not about using a copyleft licence or not, but about assigning ownership.
It's both. If you have #permissive licensing or copyright assignment (or similar), then one entity can take their ball and go home, closing all future versions that they make. If you have #CopyLeft and you don't have copyright assignment, then they can't.