Ross had assembled a huge fleet of soldiers to take out Marston. The first wave was just a warm up for them. Abigail and Jack couldn't have gone very far, as you can Abigail sending Jack back to check on John right she hears a shot and later they mourn at him being shot to death. Even if John had single handedly taken down the first lot, what's to say, Ross wouldn't have had back up fleet? I mean he was a Federal Agent after all. It was inevitable, John had to die. His past would never let go of him. Let's face it, the game needs to have a realistic approach. Part of the feature, which separates this game from having a GTA approach.