I pray to God, that he wasn't..
..I wouldn't wish that type of death on anyone (well maybe on Paul Pollis and the entire Sammy Wheeler cast....
)
1. This is kind of a trick question in that the people that killed him may not have intentionally kept him alive. Perhaps they beat him over the head, in which case he may have been alive, but unconscious. They may have attempted to kill him, but didn't do the job effectively in which case, David was alive.
2. Using a gun, would have aroused security, so unless they used a knife, I assume it was a blow to the head type of job.
3. I don't care how suicidal you are...NOBODY is going to committ suicide by going into a furnace. That's like a construction worker committing suicide by going under a cement mixer. Or a diver deciding to committ suicide by jumping into a pool of pirhanas. Or a firefighter deciding to committ suicide by jumping head long into a blaze. There are OTHER less painful and more effective ways to committ suicide than by lowering yourself into a nuclear furnace.
4. Keep in mind the purpose of his attackers dumping him into the furnace was to destroy evidence. They weren't trying to be cruel as much as practical.