The question seemed easy enough: We’ve dropped a user, now we want to change the DEFINER on all database objects that currently have it set to this dropped user?

This should be possible by checking the INFORMATION_SCHEMA tables of the appropriate object types (routines, triggers, views and events) and performing an ALTER on each of them that just modifies the DEFINER but nothing else, right?

Unfortunately it isn’t that easy, or at least not yet (see http://bugs.mysql.com/73894 and https://mariadb.atlassian.net/browse/MDEV-6731 ).