Change role of users after deleting referred content via rules I added an entity reference field to user referring to a type book. 

I also created a rule that each time e user update that field, selecting one book, his role changes from authenticated to reader.
So let's suppose there's a book and five users pointing to that book. These five users are readers. What i would like to do is that when that book is deleted, those 5 users role change into authenticated, being no more readers.

What i need is a way to reach the referencing users when deleting a book.
I think adding multiple reference field from book to users could be kinda dirty, because there's already a connection between book and reader.

I've already created a rule that when a user change his book field, selecting no book, his role reader is revoked. I hoped that in this way, considering that when i delete a book all the users referencing to that book change automatically their referencies, their role can change too, but unfortunately it seems that this is not considered a "After updating an existing user account" condition.

How could i do that possibly using rules? If it is possible, but not via rules, can you explain me in details how can i do?
I think i resolved it by using "fetch entity by property" and looking for the entity reference field that is equal to the current removed book.
Doing that create a list that you can iterate with the loop and inside this use actions to revoke roles.