If the shaft isn't opening the valve and the shaft pulls out then it probably has separated from the valve as Chris-PA as said. I would first try turning the handle in an attempt to rethread the shaft in to the valve. Who knows maybe it was loose and over time finely unscrewed itself. If that doesn't work then he might be able to insert a long bolt with coarser threads into the shaft opening in an attempt to get it to bite hold of the valve. Of couse he will then have to replace the whole valve but at least the tank will be empty. A valve change out isn't hard. Its four bolts and a gasket on either side of the valve.
I can't resist this but it sounds like a crappy job.
I hope it turns out okay.