3. Knock them down and leave the space empty. There isn't any option for rent collection and knocking the buildings isn't free so this could prove more costly in the long term.
Most of the buildings were knocked down especially on the Altrincham line in BR days to create parking space, what remains are the platform side former platform building walls, though there are a few where the rooms are just sealed but intact except for floors.
The Altrincham line buildings are quite nice and worth saving at least the facades, the Bury line buildings though tend to be 80's style cast concrete structures which are deteriorating heavily. The brick cladding thats going up on some of them is a vast improvement.
Comes back round to the same problem you have on a lot of BR stations, platform buildings having a step up from platform height or if the platform levels raised are below platform height. To raise platform height you have to demolish the platform buildings sitting on them.
