This might have been my typo and should have said mod-email.
That said, I have retested with mod-email-1.6.0 not sender) and the
tenant schema for the module is correctly purged fro the DB

@Wayne Blair,
the mod-sender doesn't use DB. Could you please clarify what should be cleaned after module disabling?

More information from @Wayne Blair:
I found these problems when testing the steps to delete a tenant.
tests failed because the tenant was not completely deleted from the database and left a mess that had to manually be cleaned up. That's fragile and one could easily delete the wrong thing.
I would give this a high priority because all modules are suppose to manage this detail and should not require going under the covers to get direct DB access.