1999 Chevrolet Blazer drivetrain & axles problems

I had to have the driveshaft in my 1999 chevy blazer replaced in march 2011. Exactly one week later my son was driving to school cayuga-onondaga boces in aurban when the drive shaft fell out causing the blazer entire rear-end to seize up throwing the vehicle almost making my son go down over the bridge. The school came and towed him back and looked at it' the bolt that holds the driveshaft in was not there, as if they forgot to tighten it or forget to put it on all together.

While driving 25-30 MPH vehicle jumped out of 2-wheel high into 4-wheel low. Conditions caused the vehicle to skid two car links before stopping. Vehicle was towed to a repair shop, and mechanic replaced the transfer case motor and the electronic module. Dealer and manufacturer were not notified.