Was just watching this movie again and I noticed (in the movie, don't know about real life) Rob seems to give up after Doug falls off the trail. Like once Doug was gone all the fight went out of him.
"Listen, I don't tan, I don't burn, I implode."
I considered that as well. He took his duties as a climbing guide very seriously, and when Doug went, he seemed to be devastated.
But then again, he may have been pinned down by the blizzard. Remember, he was at the top of the Hillary Step when Doug went. That's a very steep descent, and probably not doable in a zero visibility situation.
My take is that Rob was still way too high on the mountain when the blizzard hit. He was still in the 'death zone', where oxygen deficiencies slowly kill the body.
His decision to let Doug summit essentially cost him his life, and his mate Harold's as well.