If we delete a resource (or role), the approval workflows about the deleted object remain in the approver's task list.
However, if the approver tries to view such a task, he gets a nasty error on the Web GUI. We (the administrators) have then to find the running workflow in iManager, and terminate it manually.
It would be nice, if the deletion event of a resource (or role) would atomatically terminate all its running approval workflows.