The contractor came out to survey the damage early this morning. When I asked about the walls caving had they been up, he said "Most likely, as they would not be supported by floor and gravel and drains yet..." then went on to explain that that had already happened once to him earlier this spring. He indicated that this was what they were fighting all the time for the past two years.
The plan now is to dig it all out Monday (weather permitting) then proceed as possible. Obviously, the crew will NOT be coming on Tuesday as planned. After pouring, it needs to cure for three or four days before the rest of the room goes on top. We'll see if the visitors will be treated to snow or not before they get home.