I think it would be useful to be able to search for users who have not (yet) accepted the privacy policy or terms or who last accepted within a given date interval
Would it not be easier be easier to log everybody out?
That way they would have to log back in and accept the cookie notice in doing so.
I don't know if xenForo has the option to do this, but if possible it would be preferential rather than deleting members or risk having your email address added to a spam filter due to the number of emails you would have to send out to tell everyone to accept the notice