It will definitely be difficult to use the building again for something else, given the fact that the entrance has to stay where it is due to the building being set back from the park, the fact that there is clearly something on the ground floor of Pirate Adventure hence the ramp climbing up, and the fact that the small upper section couldn't really be used for much else again.
It will certainly be difficult to repurpose the building for much else other than a free flow, unless of course they decide to disuse the upper section completely and have an entrance from Thomas Land behind Rocking Bullstrode into the lower section of the ride... There is no way of entering from the main park other than through the main entrance, which clearly uses ramps to gain height to avoid something on the ground level of the building.
Not to mention that the ride clearly used a lot of concrete from looking at the auction catalogue, it looks like the scenery was built on concrete, and the concrete then dropped into the water filled sections, that's a lot to fill or remove if they wanted to repurpose the building. Don't think it'd be worth it myself.
The tracked parts are the drop, the unload section, the lift to bring the boats from the unload to the load station, and the load station itself. The rest is just pumps at the bottom of a metal trough, I presume from looking at other similar ride systems.
There's been an all around positive reception to Gangster Granny: The Ride at Alton Towers, this clearly shows that there is a demand for a family dark ride in the UK, and Drayton could certainly out do Alton Towers with the space they have inside Pirate Adventure, let alone with a far superior ride system. Gangster Granny builds the dark ride hype in the UK Industry ready for Drayton, if anything....