If Jason was worth anything he would voluntarily leave the Cowboys organization to make it on his own. He had 10 years and never really sniffed a SB threat.
There is no way JG can come back as HC because the fans would revolt and merchandise sales would drop to near nothing. What I think is happening is that Jerry Jones is trying to find a way for JG not to go to coach another team because if he did and he had better success then that would be really bad for Jerry.
Jerry Jones has said many times that he did not want to give up on JG after investing so much developing him. He has said JG would immediately be hired by another team and he did not want to see that. This is about covering Jerry Jones at this point.