Well, since you're not a new comic fan you'd know that they could bring back Gwen Stacy. Over in Friendly Neighborhood Spider-Man there is an alternate evil Uncle Ben running around.
And lets not forget that somewhere out there in Spider-Man limbo there is a Gwen Stacy clone. So, yes, technically they can bring Gwen Stacy back.
And ALSO Jeph Loeb/J. Scott Campbell had an ongoing Spider-Man book scheduled sometime this year and it had a lot to do with past Spidey stories, like those stories with Gwen Stacy.
So, yeah, she can come back and trust me she probably will come back in some way. Whether it be through flashbacks or what have you...it's in the movie it's gonna get covered in the comic. It happened in the first Spider-Man film. It happened in the second film. And it's gonna happen here. Don't...be...naive. If they can bring back Bucky and Uncle Ben. They can pretty much do whatever they want.
Never say never.