This is probably way out there from other peoples' thoughts about the ending, but this is what I think will happen: Venom kidnaps Gwen Stacy (of course Eddie will wanna kidnap the girl that he thought he loved), and Venom, Sandman and Gwen is ontop of a building waiting for Spidey.
Spidey finds out that those two powerful enemies are waiting for him, so he tries to plead with Harry to help him, but Harry says no, so Spidey has to fight the both of them himself...he gets his butt handed to him, Venom and Sandman are way too powerful for him, and then Venom decides to kill Spidey right there, but a hammer forms from Sandman's hand, he knocks Spidey off of the building, Venom gets upset so he grabs Gwen and throws her off, Venom and Sandman get into an arguement/scuffle about each of them wanting to be the one who kills Spider-Man.
As Gwen is falling, Spidey sees this, uses his webbing to save Gwen (like how Spider-Man uses his webbing to save Aunt May in S-M 2) and gets her to the ground where Gwen tries to kiss him again and he backs away saying no, and Gwen just looks on while Spider-Man comes back up on the building, but sees no one ontop of the building...then we go to Harry's place where MJ comes in and asks Harry to help Pete because he needs help, so Harry, still mad over Pete killing his dad AND the fact that Peter threw a pumpkin bomb at him earlier, he still says no, but then decides to be a man and not listen to his father anymore, so he dones his suit and flies off in his flying snowboard to help Pete.
While Harry goes to the scene to see that the fight has moved on to a construction site, he goes to help and he starts fighting Venom at first. MJ comes in the scene now, in a taxi, and the driver sees a huge sand figure coming to get the taxi cab, the driver bails, which has MJ still in it...then he tosses the cab which has Spidey coming in to save her, but with Harry knocked out, Venom uses his webbing to save the taxi before Spidey does, and then they fight, while Sandman starts to fight Venom because he wants to kill Spider-Man...it becomes a triple threat fight, with Venom biting Sandman's neck, and it's almost like poisoning for Sandman, so he drops to the floor, but doesn't die since, well, he's sand and all, but he's down for the count on the pavement...it's then Spider-Man vs. Venom, with them fighting and moving back to the construction area, where Harry awakens and gets into the fight, with Spidey still getting his butt kicked, and Venom ties Spidey unto a beam, and about to finally kill him while Harry comes in and fights Venom off, but now Venom grabs a beam, rams it into Harry's chest and kills him, as to where it shows the scene of Mary Jane looking out the taxi, he sees Harry fall to the ground, dead.
Spider-Man then tears the webbing off, and gets so angry, he even nearly kills Venom, but then he starts to bang beams together, making a loud noise that leaves Eddie's body, so Eddie then charges Spidey one more time, and he also gets impaled into a beam, the symbiote goes after Pete, which he fights the symbiote off, and while the police is coming, the symbiote flees, sinking itself unto the floor and into the sewers...Peter gets MJ, then go towards Harry while the police arrest Sandman who's still down and Gwen meets up with her dad...and yah, that's what I think will happen. I doubt Pete and MJ gets married, just, re-start their relationship.