Thanks for the great pictures, Tim.
The strength of the interior walls is what has held the old structure up all these years, but what your pictures don't show is that the exterior structure has deteriorated into the ground, and can't be leveled, straightened, or raised. Also, the entire roof structure is in need of replacement, and it can't be replaced until the walls are straight and true, and that is impossible.
An unfunded engineering assessment was done back in the 80's, and this was the determination at that time, I'm sure it hasn't improved with age.
The owner, the same person that owns the Eating House, has obviously not spent any money on upkeep, perhaps you should approach him for more information.
Good luck~