I have one case where the v1 and v2 of a module are simply incompatible, but v1 still works, and unless the users have a compelling reason, they won't migrate. Pulling the rug from under them would be quite unsportsmanlike.
Deletion should be opt-in, and there should be a way to "pin" some releases as unreapable. And warning emails (yes, some email addresses are blackholes) to the author well in advance: "your module X version Y will be deleted as you requested in Z weeks because there are P newer releases ..." -- There is this special biologist word we use for 'stable'. It is 'dead'. -- Jack Cohen
