Various thoughts on the subject.
Fans are horrible at guessing at how these things end. How many people saw "no more mutants" coming? or Osborn taking over Shield? Or Magneto as Xorn? Or Echo as Ronin? How many people saw the skrulls? And so on.
Fans are assuming that Osborn will be removed from Hammer, but I'm not so sure. If removed, Osborn really no longer has a place at the Cabal. What will you do with the character then, make him the GG again? Marvel is trying to evolve the character, but all fans want to see is regression.
Is Hammer/Osborn really going to have that short of a shelf life? Has Marvel already used up all the ideas there? What will happen to other titles like Secret Warriors, Dark Avengers, and so on? At some point, I'm sure Fury will become head of Shield, but is the time now?
Osborn became a Marvel Universe villain, moving away from just being a Spider-Man villain. I don't think Spider-Man will bring him down. Even now he is just an occasional villain for Spider-Man when they want a boost for the title.
Iron Man vs Osborn? Well Stark is in no position to battle him. Would people really care if that was the climax? Then again, he does have a movie coming out next year.
One way of looking at it is "which character does Marvel want to promote?". In that case, either Iron Man or Spider-Man would fit. IM because of his movie, and SM if only for a sales boost.
Captain America vs Osborn? Cap has alot on his plate coming back to life and all. It's an idea that everyone sees coming, and maybe it's a little too obvious.
New Avengers vs Osborn? Strong possibility since the title is heavily involved in the storyline. NA vs the DA team will be a big event. It also makes sense for the biggest property to be the focal point.
Reunited Big Three vs Osborn? Well they just did the Big Three reunion in SI somewhat. And one you do that, they have to be all together in the Avengers. I don't see that happening now, but probably closer to the movie in 2012.
Cabal vs Osborn? Well we've seen the others plotting against Osborn for a while. Hood and Loki. Loki and Doom. Doom and Namor. Namor and Emma. Wouldn't really be surprising, but it would easily turn into a melee with everyone betraying everyone else.
I just don't know, and really don't have a guess. I'm guessing it's going to be something none of us thought of. I'm not even sure I know how I would do it.
More to the point, what you're saying, essentially, is that Dark Reign doesn't end. Presumably the "Dark Reign" has to refer to somethign going on, be it the Cabal meeting behind the scenes or to Norman running SHRA enforcement, and the end of that situation would be the end of Dark Reign.