I don't hunt in grizzly country, but if I ever do a hunt where there are grizzlies, I would probably want a shotgun with buckshot & slugs or something like an AR10 in .308 as part of the equation if working on a downed animal. One in the barrel and a full magazine. I would want something that will kill the bear asap, not deter it.
As far as pistols go, I have read reports where trained police officers have fired every round from their service pistol in a CQ (about 10 yards) shootout with a thug, and never hit their target, and this is a trained police officer. Shooting a pistol under the stress of a charging 800+ lb killer with sufficient accuracy is probably a pretty tall order for most of us. I have read a grizzly can reach speeds of 30 mph, that is about 44 ft / second. Not much time to react.
Very sad news about this guide, husband, father loosing his life this way.