And, the guy had an unregistered firearm, according to the warrant. Cops would have approached him as a threat to begin with. If he had not resisted his arrest, he would not have been a threat, and it would not have prompted the officers to take any further action.
EDIT: In other words, he wouldn't be dead.
What makes you think it wasn't taken away from him like every other unregistered firearm is?
What kind of question is that?
The point is, he resisted. The cops knew he was trying to get back into the vehicle and flee. When you flee in a car, you make yourself dangerous to other people on the road.
If I were a cop and saw he had a warrant for his arrest for having an unregistered firearm, I would approach him with extreme caution.