Should be easy - just compare to any public employee or low level government employee. ie) average Americans.
When you leave a job, do you get to keep your computer access? access to trade secrets? company files? financial information?
Hell No!
See Hammerhead’s post 36, regarding the difference between clearance and access.
I’m not trying to suggest that the characters originally under discussion should keep - or should ever have kept or even HAD - their clearances; just suggesting that there are useful reasons for extending clearance (not access) beyond separation for a defined period of time.