“”How long do ex-officials get to keep a security clearance?””
It depends on which party they belong to.
Honestly, I can see Obama and JF Kerry having one. There may be continuing programs and issue that they need to be asked about. At least durring Trumps first term. You have to agree with their policies to possibly need to talk to them about things.
Comey was fired which is a different thing an administration change.
Anyone who was fired should have their clearance cancelled before they’ve finished cleaning out their desk.