If they lost a windscreen, they'd get a 400kt blast in the face of air at -40C or so.
Getting your mask on and establishing comms as per the checklist would be challenging to say the least. They may have initiated the descent but a 400kt breeze could easily rip the mask off your face. The noise would preclude any communication either in the cockpit or with ATC.
It would be a terrifying enough scenario without considering the possibility of potentially fatal consequences if the windscreen, or parts of it, came back into the cockpit. The cold air and wind may cause you to keep your head down below the coaming. If that was the case, you may not recover in time to look up and see the mountains looming large...