I assume these would be resolved tickets? We are going live next week (after months of dev) with WHD and this is how I plan to handle it:
-When the ticket is resolved they will get a resolution email giving them the opportunity to confirm the resolution or disagree
-If they confirm it the ticket is automatically closed
-If they disagree with the resolution the ticket is automatically reopened
-If they do not respond within a certain time frame (still tbd) the ticket closes automatically
As far as a rule this is how I'd filter the tickets but not sure how you're also filtering by client update date.
I'm sure theres a lot of other ways to do it but as a help desk manager I guess I'd want to know why they are stale in the first place.