There's been some speculation over on TS that the N:ST drop towers have been removed, obviously I can't confirm the accuracy of that. If it is true then it could be possible it's for a major overhaul, or with the rumours that have been going around it could be permanent.
Personally, I don't think we will be seeing a return of N:ST, which would be a real shame. Of course it was marketed ridiculously as always and it was a bit naff, but all of that aside it was a decent indoor attraction and it offered something a bit different. The building, theming and queue line really looked the part, a stark improvement over the trampolines and Lava Lump that had greeted you upon entry to Forbidden Valley for many years.