From the pictures I saw, especially the full 50 gallon trash can upstairs serving as a collection bucket for a roof leak, and all the obvious water damaged plaster/lath walls and ceilings up there, it's obvious the roof has been leaking for YEARS in multiple locations, by now the water has done so much damage up there I'd bet if the plaster was removed they would find almost every roof rafter has rot, and the walls too.The top floor floor certainly as well.
Unfortunately once a building's roof is breached and left that way, it's pretty much the beginning of the end of the building, those softwood studs, lath, joists, rafters and floorboards start decaying amazingly fast and once it starts it proceeds rapidly.
I remember an abandoned building in NYC that had a fire which burned the roof off in one area, they cement blocked the windows and closed it up, but a tree grew up on the top floor that had a trunk that was 6" in diameter. The weight of a brick slid across the floor was enough for it to fall through the floorboards.
I don't see this building being renovated, the costs are too high and they could only fit a small number of say, apartments in there, and people will only pay so much for rent.
But if anyone wants to save it, someone had better deal with that roof ASAP and stop the water from coming in before it really is too late if it isn't already. Someone with a couple of 5 gallon cans of trowel consistancy tar and a roll of tar paper could probably temporarily patch most if not all of the obvious leaking spots and buy it some more time, another year or so maybe.
Once the roof deck and floors have rot it would likely have to be gutted to the bare brick shell and all the interior walls, floors, electrical, windows, plumbing, heating, stairs etc etc would all have to be replaced.