There must be something more to the story, like him trying in some kind of ways to take advantage of the fbi without their full and clear agreement. So whenever he can post without jeopardizing his own situation, then we'd be able to really find out where he screwed up for the fbi to turn on him.
Could be, but I think the Feds are mean enough and try to screw the informant once he served its usefulness without any extra reason. After all the deals are usually made verbally, or there could be a new prosecutor who doesn't honor the agreement, etc.
Sorry I don't believe so : what would be the interest of this agency to turn against an informant, except if the informant tried to cross them. They have a hard time recruiting informant, so does not make sense to mess up an informant that is reliable.