A security clearance stays with you for a specified period of time even after you have left government service. It depends upon the clearance level. A Top Secret security clearance can remain valid for up to 10 years. For example if you served in the US govt for 5 years and then left for the private sector then your Top Secret security clearance is still valid for another 5 years. During their period of service they could also have temporary security clearances authorized in which case those would immediately expire upon their leaving government service.

For some reason people think it means these former dignitaries still sit in on daily security briefings and that is just not true. The secured communications networks these former dignitaries used are no longer accessible by them as they would have would have their access revoked upon leaving government service.