[VariousRen]

So the actual math for figuring out what's going to happen is beyond me, but I can give a few insights from low level structural engineering classes I took early in my degree.

Stone is strong in compression, but it's hard to find mortar that's any good under tension. If you just had a floor made of stone bricks with mortar between them, it would almost certainly fall apart under it's own weight with any serious span. More likely, the stone tower either had:

1) a shallow dome (arch in rotation) that supported the 2nd story floor, which would be visible from the 1st story. This turns the tensile stress on the mortar into compression stress on the actual stone. Removing part of the dome would be a bad idea, the floor should be heavily compromised. Note that even if the floor collapses the walls of the tower will remain standing, and the upper floors will be fine.

2) A wooden framework that supported the floors on each floor. Looking up from floor 1 you would probably see a grid of wooden beams (maybe covered in iron, if you were worried about people taking the bottom of the tower and hacking at them from below). When stone to air was cast the stone would have been removed but the wooden supports would remain. The floor should be fine, as long as no fool goes around and hacks up these support beams too.