I'll take the middle of the road, here.
I think the Marvel films are going to be around for a looooooong time and make a lot of money for Disney. For the last few years people have been saying that the genre is played out. Yet it's entirely possible that Avengers and Dark Knight will finish 1 & 2 at the box office this summer.
Marvel did just an amazing job of bringing all of these characters together...orchestrating the different character tie-ins throughout 4 peripheral films (IM, IM3, CA & Thor) over a period of 4 years. And they've had the foresight to sign the actors to long term deals. Based upon what I have read, Mark Ruffalo is signed to play Banner in SIX films. Chris Evans' deal is also for six. Samuel L Jackson's contract was for NINE pictures.
Some people will tire of super hero action films but saying that the genre is burning-out entirely is a bit like saying that audiences don't want to see police dramas anymore or organized crime dramas or raunchy adult comedies. $200 million in three days suggests people will turn up for quality entertainment...even if it is popcorn fluff that won't be nominated for best picture.
As for theme park potential, I think Marvel is best suited as a single land within a park. The appeal of Marvel properties will ebb and flow with things like film and DVD releases.
I always thought it would be a great fit for the Streets of America section of Hollywood Studios. Retheme it to be a sort of Marvel-ized NYC. Fill the streets with a variety of Marvel "Easter eggs" and interactive elements, while adding a couple of attractions and a restaurant to the surrounding area.
But of course that pesky contract stands in the way.
As for the contract having some ending date in the near future, I'll believe it when I see it. It wouldn't surprise me one bit if the Universal Transformers attraction matches Spider-Man. That would have saved millions in development costs by not having to engineer a new ride layout, fabricate new parts, etc. Developing these attractions isn't like Rollercoaster Tycoon where you pick a straight or curved piece of track.
Disney would have to formulate some dramatic plan for use of the Marvel characters to even entertain termination of that licensing deal with IOA. Right now Universal pays millions per year in licensing fees and Disney / Marvel does absolutely nothing.