I think Jack would be pretty pissed off. Why?
Well, firstly, George Mason was behind the nuke attack in S2. He was never exposed to plutonium - he was faking it. He meant to get on that plane and was hoping to kill Bauer in the blast.
He managed to get the nuke parachuted out of the plane. At the very last minute, he managed to get the plane to 88mph which activated the flux capacitator
George Mason was then behind everything that happened since, altering time and space to fit his own warped ideals. He timetravelled to when Nina was killed by Bauer. At the last minute, seconds before the gunshot, he swapped her body with a double before flying away with her in his plane which now has a delorean attached for road use
So yeah now he's like shit son dye your hair blonde and lets have a kid and Nina is like yeah sure ok