If they really stayed with him for 1.5hrs and even left a man behind with him until he started running low on oxygen, then what else could they really do? How realistic is it to call for a helicopter on a mountain during weather conditions so dangerous that even the guy who recorded the video decided to cancel his ascent?

It's tragic, yes, but mountains don't fuck around. For every 4 people that summit K2, 1 person dies trying (source). It's ridiculously dangerous. Going on what's in the article, even if you don't believe the climbers when they say they tried to help, I have a hard time seeing any outcome where this guy makes it out alive.