The only reason not to tear Rockit down is that it's immensely popular, though I have to say, lame as all hell. First time I rode it I thought it was cool, but it has not held up well at all.
I don't see Universal removing Rock-It before trying some other options to remedy the reliability problems.
Coasterforce and a few other sources have reported that engineer from other coaster companies besides Mauer-Sonne have been spotted at the attraction measuring the track for a possible retrofit to more traditional trains which would increase capacity and reliability for the ride. At any rate, it's the Studio's only visible coaster and a likely draw for the park. I know that when I was there this summer its presence was the main factor in convincing me to visit both parks instead of just Islands (even though the ride turned out to be a disappointment).
Building Potter into the original park makes absolutely zero sense. It would kill the novelty of it in IoA and would be overkill on so many levels. It's not going to draw more people to Universal. Any Potter fan that wants to experience WWOHP is going to do so anyway. If anything, it will turn people away that would think it's too much Potter. Believe it or not, not everyone likes HP.
I don't think this is necessarily so.
For one, if box office and merchandise performance is any indicator we have yet to discover a point at which there is, "too much Potter".
If Universal were to make the ad campaign clear enough it wouldn't be that difficult to explain that the Wizarding World would become a 2-part experience, with one being the "Hogwarts/Hogsmeade" area and the other the "Diagon Alley" area. People wanting to see all the Potter stuff would then buy a 2-park pass instead of a single. It could work very well if the arrangement is made clear enough.
That said, even if it would work I think a Potter expansion into the original park isn't the most likely theory here, when it's all but announced that Potter phase 2 is going to involve a refit of the unpopular Poseidon's Fury building and surrounding area.
I think Transformers is the most likely bet here, followed by Madagascar.
Madagascar would actually make more sense from a planning perspective because the Studios is arguably lacking in kid-friendly attractions right now.