to go by that theory we have to accept the idea gwen won't die this film, because a cameo from MJ "face it tiger" wouldn't fit in well after a scene where peters gf just died
and even if gwen doesn't die i'm unsure how you could bring MJ in as a cameo without almost feeling like an obvious set up for gwens goodbye, alot more then introducing her early
i don't think webb was ever going to do a love triangle because when you have gwen who everyone pretty much suspects they will kill off, its abit disrespectful to the character, i mean yeah maybe it happened in the comics but to make what happens to gwen tragic you can't do that, when there is MJ it may take some of the tragic factor away for audiences