This might be an unpopular opinion, but I think Terminator Salvation would make the best scenario for an open world survival/light mmo type game. Unlike all the other movies, this one had all kinds of different enemies: small snake and eel machines, human size terminators (in disguise or just bare metal), objects that turned into terminators (motorcycle) and giant mech like machines (raid or open world event boss). I can imagine our characters leveling up and getting endgame missions from John Connor.