This failure mode is very expansive for us,
I get it, it's actually cheaper for you to store the unused disposables and notes than it is for you to [potentially] have some more emails to forward. OK, 'nuff said, I'll never ask for this again.
...periodically scan our tables for disposables that are (1) hidden, and (2) have not received any email in 6 months...
Sounds fine to me, but if it's any trouble at all to do this, don't bother. The welfare of the service is more important than anything else.
If you DO decide to do this scanning, I hope the disposable need not be 'hidden' during the entire six months, since users are likely to reset this timer if they go through their hidden disposables while doing housecleaning on their accounts.
I can also imagine someone hiding disposables with LOW activity which they do not actually want to delete.
So...
If you decide to do this, make a check box or something so the user can 'submit' his deletion 'request' to your software. If the software agrees that there has been no activity for six months, or after waiting six months, or whatever, THEN your software will 'approve' the deletion, and the disposable is gone.
If you want to bother...