I'm not sure I understand the question. If a crew and vehicle from the future was blown up in the past, and then everyone else from the future that's alive (ie, everyone on the ship) returns at the same point that they left (minus CAG and Mrs. Robinson's daughter), why would that crew affect the future? The Senator and his aide were already dead in the original history and the CAG would just have a double for 40 years. They already established that the future WAS altered by Mr. Tideman (CAG) before they even left. Obviously time travel stories eventually end up messing something up (even Looper), but The Final Countdown is actually a reasonably tidy time travel story...except for Soon-Tek Oh and his wingman.