What really happened to Gwen Stacy?

From the word of god:

As many have predicted for nearly a year, Gwen Stacy (Emma Stone) does indeed fall to her death in The Amazing Spider-Man 2, much as she did in Amazing Spider-Man #121 – a comic which, appropriately enough, is known as “The Night Gwen Stacy Died.” But regardless of speculation and source material that dates back nearly four decades, some audiences were still shocked to see Peter Parker’s first love come to such a terrible end. “I’ve poked my head into theaters in L.A. for that moment just to hear people gasp,” director Marc Webb tells EW. “It’s fascinating. People just don’t believe it.”

Webb understands. He felt much the same way when Gwen Stacy was killed off in the comic. “It stayed with me in a profound way. It broke me. I was anxious and curious to explore it on the screen. From the very beginning I planned on doing it,” he says. “For me, everything in the movie was built around that moment. There’s a cost to being a hero.”

And since the franchise has died to allow it to be rebooted, any speculation on ASM 3 is just that, speculation. So Gwen is dead and buried.

Of course, comic Gwen was eventually cloned 2 years after her original comic death, as part of the Clone Saga. And died. And resurrected. And rinse, lather repeat as comic characters are known to do.