Sending a reminder after a process has closed

Good afternoon everyone!  I am trying to find out if there is a way on an automated process that closes after the completion of all tasks, to have it send out reminders about 30 days after the tasks are completed,  and make that part of the required completion before it closes?  I have built an HR termination process which will assign tasks to each group for deleting user accounts, however there are two groups who only disable the account initially, then after a 30 day period they go in and delete the user.  This is to assist with those times a user is actually just moving locations and it was put in incorrectly, or for those users who leave and come back within that period.  I have a calculation set on the 'send date' of the reminders thinking maybe if they won't send until that date it will keep the process from thinking all tasks are complete and auto-closing, but still once the tasks are completed the ticket closes, and of course reminders won't send.  Any ideas?