Personally, I'm a little tired of this "let's save it for the sequel" crap. For this movie to actually be meaningful, you must have a strong, unique, substantial story to tell. No more filler, no more preambles. Gwen Stacy dying would make this movie as interesting as it could possibly be. It's the story of the young hero paying the price for his nerve, the nerve to defy evil gods. And sticking by his mission even despite of that. We haven't seen that yet, because, come on, the death of Capt Stacy meant nothing to him personally. He had like two talks with the guy.
But Gwen? That's where it really hurts. And I don't want to wait for it until 2016, I want a powerful Spider-Man movie NOW, because, let's face it, this franchise needs it.
Do you want to walk out of this movie thinking "Hey, that was pretty good"... or "HOLY ****, THAT BLEW ME AWAY, I'M TOTALLY SPEECHLESS BY THIS EMOTIONAL PUNCH IN THE GUT"?
If it's Electro who kills her... frankly, I've seen fans forgive worse. Many forgave the fact that Spidey's everyman nature was removed from the character by making him a bearer of his parents' scientific legacy. Meaning that the aspect of "this could happen to anyyone" was entirely disposed of. If it's Electro who kills her but Norman is behind it, it would work for me. And it would make the 3rd film (REVENGE!) an actual must-see, instead of just a "Yeah, let's see how they do this time".
Kill her.