Not necessarily.
Regarding introducing Goblin as a background character and then having him swoop in at the end of the movie, grab Gwen, and drop her, such a scenario would completely overshadow everything else that had happened in the movie and render Gwen's death - which has gravitas and oomph in the comics (as I understand it) - nothing more than a cheap 'shock and awe' stunt in the minds of general audiences (although it would certainly get them talking). In order for Gwen's death to actually mean something to general audiences as well as to comics fans, it has to be built up to in all aspects.
- I think we all expect Norman to be in ASM2, yes?
- I think it is fair for us to expect that Norman will be on his deathbed at the beginning of ASM2, since that was what was inferred in ASM1, yes?
- I think it is likely that a serum of some sort will be given to Norman since much of ASM1 was about exactly that, yes?
Ok, so then Osborn will be in ASM2 AND we will likely see him given the serum that will on one hand prevent him from dying, but will also radically change him into the Green Goblin. There are, of course, many different ways they can portray this transformation. It can be a mask, it can be multiple personalities, it can be cross species, etc.
Now, what would you do/where would you go with Osborn once he has been given the serum? Do you just show him being given the serum while on his deathbed and then not show him again until ASM3? That doesn't make much sense, right? Especially when you want to use the newly signed Cooper and get the general audience recignizing/hating him.
So, do you show him being or becoming maniacal? Do you show him losing control? Do you show him talking to himself in a mirror - (just threw up in my mouth a bit)? Hopefully not since we saw that one done already, right? Now yes, we have Electro and at least to some degree Rhino (he might not get turned into Rhino until later in the movie - but he is at least some thug driving a truck, right?). So if you got some guy sucking up power, and you were this newly transformed, new lease on life, somewhat maniacal psychopath, what would you do? Would you try to get this guy on your side? Would you try to capture him to figure out what's the deal, maybe even harness the power? Who knows, but it is likely that this Green Goblin/Osborn would do something, right?
Same thing could be said for Rhino. He's going to get Rhino'd up somewhere, right? Isn't it likely that Osborn/Green Goblin will either be behind it or at least involved? Won't GG want to use Rhino?
The point is that Osborn/Green Goblin is likely to be ramped up big time is ASM2. To me this build up seems to be GG as a mastermind, right? So he will be the big and bad villain in ASM3.
One thing I am somewhat worried about, or excited about the possibility, is Webb throwing a surprise in there. We all expect Osborn to be GG. I am almost positive we'll be shown Osborn "becoming" GG, to some degree. So when we all see the Green Goblin with a mask on we'll all know it's Osborn right. Now what if when he removes the mask it's instead Harry? I am concerned that Webb would love to pull a switcheroo like this on us, but hopefully he'll just stick to canon and go with the expected...
Look , we all agree that sometime between the end of ASM2 and the middle of ASM3, Gwen is dead, right?
Think about how much hinges on her death. The MJ friendship, revenge against GG (assuming and hoping that it will be GG), the audience hating GG, solidifying GG as a heavy hitter, Peter having to deal with the fact that his action helped cause Gwen to die (if they go that route, which I think they will), etc.
So, if they do it mid way into ASM3, can they really get into all of this? Maybe, but not very well.
But if they have her die as the finale of ASM2 then the whole of ASM3 is set up. To some it might come off as a cheap "awe and shock" tactic, but for most of the general audience they will walk out of there actually is awe and shocked. They will be saying "wow, I can't believe that happened". They'll be counting the days until ASM3.
The funniest thing about all of this discussion is that I've realized one thing...
If it wasn't Emma Stone as Gwen and instead someone who was just ok, most wouldn't have these concerns. Now imagine that Emma was MJ instead. Most would be like, heck yeah, bring on Gwen's death so Peter can get with MJ. Hopefully you get what I'm saying. So much of this resistance to Gwen dying sooner than later is because we all love Emma so much. Believe me, I do too! But Gwen's fate is what it is... They can't keep her alive and they have a story they must tell. And this includes MJ and Peter becoming closer, finding out the deal with Peter's pop, the whole GG thing, and so much more.
If you search your feelings you'll see that Gwen dying at the end of ASM2 makes the most sense.