At 32,000 feet, a missile would have caused an “Explosive Decompression”. The sudden loss of cabin pressure would have caused severe injuries to the lung and incapacitate many organs. Yes, it would have been quick. In fact, many would not really know what hit them.
Certainly this is scarce consolation to the families of those lost on this unfortunate flight. The intention of tracking a plane with the intent of destroying it, without proper verification of its status was devious.
The quick death is scarce consolation.