Do creatures that fall from the removal of a stone bridge created by a wall of stone spell get a save

The example given in the spell specifies that "dirt" is ok. I feel as though this line is being taken out of the context it's written in. Here is the full context.

The wall doesn't need to be vertical, or rest on any firm foundation. It must, however, merge with and be solidly supported by existing stone. Thus, you can use this spell to bridge a chasm or create a ramp. If you create a span greater than 20 feet in length, you must halve the size of each panel to create supports. You can crudely shape the wall to create crenelations, battlements, and so on.

As long as the stone wall is merged with and coming out of a stone from which the wall can be made, it seems that are ok. I can't imagine that there exists a chasm which is pure stone without dirt, from which the spell is describing when it says you can create a ramp or bridge out of the wall.

As an evocation rather than a conjuration spell, it makes sense that the wall might require some stone to work with. This has been confirmed by Mike Mearls, that some sort of rock is required:

‏@wax_eagle : @mikemearls Can Wall of Stone be cast on dirt? It seems like its written to always need stone to merge to. Is that correct?

Mike Mearls : @wax_eagle that's correct - need some stone to merge with or be supported by. for instance, a bridge is OK if the two ends touch stone.

Daganev : @mikemearls @wax_eagle So no stone walls on a grassy knoll?

Mike Mearls :@Daganev @wax_eagle Correct, you'd need rocks of some sort (ruins, boulders) to support it.

Yes, because of how the rules on shapable walls are written

The rules for Wall spells stipulate:

Some walls can be shaped; you can manipulate the wall into a form other than a straight line, choosing its contiguous path square by square. The path of a shaped wall can’t enter the same space more than once, but it can double back so one section is adjacent to another section of the wall.

There would be cracks at a couple edges of your prison (letting in air and potentially important to the narrative), but you are able to perform as many 90 degree turns as you wish; there doesn't seem to be a limit on if those squares are on the same axis.

I would lean against it, as GM

The 7th level spell Force Cage provides a similar (albeit improved in flexibility) effect as using Wall of Stone as such which makes me think that the exact effect is probably a 6th level spell-equivalent effect. See also the 6th level Reverse Gravity which provides similar but different area control. If a player was particularly interested in using the spell as such, I'd likely allow it as a bonus effect if the spell was Hightened, though.