Sam was a ****ing mess in Double Agent and much of Conviction because he missed his daughter. Now that he has her back, he's got his humanity back...and I think he's got a voice on conscience too. We kinda saw how Sarah is the voice of morality for Sam, because I don't think he even thought about going to the White House until Sarah pleaded with him to help Grim for saving her life. He was willing to avoid the White House after the helicopter crash too, but again Sarah convinced him he needed to get to the White House.
I can see Sam working for Third Echelon again. Being brought back to wipe out Black Arrow and track down the Migito organization. We know Sam came into the Black Arrow facility to get Vic out...but who knows, maybe he's doing it officially? With support from the President.
I think Third Echelon will still live on, and this time the Director of Third Echelon will probably be Grim. She will probably replace Lambert as the heart and soul of Third Echelon, continuing to build upon what he started and try to redeem the group for what Reed did with it.
Third Echelon could become the left hand (if the Secret Service is the right hand) of the President of the United States, too. So, instead of them needing to go up the food chain and get apporval from the NSA itself or the Secretary of Defense...maybe Sam and Grim will have a direct line to the White House and take they're orders directly from the President.
That could be really cool.
The sequel could start out with Sam breaking Vic out, and then being wooed back by Grim and the President to then start to track down Migito. I think it was a very smart move, and I loved how they pulled it off, to bring back Sarah. Sam needs her, more than anything. I think her return leaves room for Sam to return to wetwork jobs for the government. I could see Vic joining in too, I really liked him.