We have several subscriptions in our databases that are linked to non existing searchrequests. I don't know why it occured, but the result is that e-mails "Subscription: Error" are sent to several users every hours and we can't delete the erroneous subscriptions because we cannot see them in JIRA since there is an integrity problem.
I think that this request is the same as JRA-3720, but you didn't understand it clearly the first time.

Could you add an integrity check that will delete subscriptions that are linked to non existing filters ?