Ok,I'm a HUGE Venom fanatic,but I think he's dead and won't return,untill the series is revamped,that is.
However,after watching Spider-man 3 today I started to think that maybe they could pull off his return. It might ask that people suspend disbelief a bit,but it's a comic book movie. I'm sure people could do that.
Anyway,Peter has Venom trapped in the circle of iron pipes and is causing the symbiote to go crazy because of the sound. The symbiote could've sensed that it might be separated from it's host(Eddie)or maybe even be weakened so much that it's killed. It needed to keep on feeding off the hatred and anger inside Eddie Brock(which makes him the perfect person to bond with). Then Peter webs Brock and tries to pull him away from the symbiote.
Now,the symbiote is a living creature,and just like any living thing it will do anything to survive and to protect itself. It has bonded completely with Eddie and knows all about his DNA makeup,so in a desperate move the symbiote creates a new "version" of Brock and takes the real Eddie and throws him clear. Knowing that Eddie will live to fight another day,the symbiote can also sense of small part of itself in Dr. Connors lab. When the time comes that small sample will seek out Eddie and bond once again to become Venom. That is the best thing for it's survival and it "knows" that it must sacrifice itself in order for Brock to live.
Peter grabs the pumpkin bomb and throws it into the symbiote. Now,the "fake Brock" that has just been pulled clear leaps in to try and save the symbiote(fake or not,the symbiote is now part of Eddie). So,the symbiote and it's version of Eddie are destroyed.
Hiding all along,the real Eddie Brock is watching all of this and sneaks away. He is utterly depressed(and furious)and thinks that his best chance of getting revenge is gone. He failed. Little does he know that the small piece of symbiote in the lab will escape and soon find him.
The opening of the 4th movie should be just like the comic. Peter,thinking everything is ok,goes to visit Aunt May. As he enters her apartment,May tells him,"Peter,a friend of yours stopped by. He says he knows you from work?" Peter,a bit confused,looks around the corner to see Eddie Brock sitting in the living room. Peter is shocked as Eddie gets up and walks over toward Peter and extends his hand. Looking directing into Peter's eyes,and flashing a twisted smile,Eddie calmly says,"Hey,Pete. It's been quite a while. You never call anymore!"

