Thing is, his “threat” isn’t about what he knows re national secrets etc, it’s about what he knows re how information is gathered so that doesn’t neccesarily make him a valuable information asset for foreign powers, just a valuable irritant.
As far as intercepting flights etc, if you’ve got an international terrorists or mass murderer or something then it’s more likely to happen than when it’s someone who’s just told an inconvenient and embarrassing truth about how shit your country can be. I think they’d rather have him pass into relative obscurity, his secret is out and extradition and trial will keep it in the public eye.