I guess Jeff Sessions was given the choice of being the one to take down all his old friends, or to ride off into the sunset after doing his duty. If that is the case, I might pick what he did.
The other issue is that having been in DC so long, he knew where the bodies were buried and he knew who to ask when he did not know. It would be very easy for those charged to start calling him as a witness and such to conflict him out. If you get someone who has not done much in politics, that problem goes away. Anyone who's had a private meeting with JS for his whole career and gets brought up on high treason charges is going to swear to god that JS was told they were really on the path of Truth and Light. Anybody he's ever sponsored legislation with is going to have a conflict. He really does need to be out of there if what Q is implying is true.