With a metre or more of snow falling, assuming he'd be right next to the road isn't logical, he could be any distance from it.
When I was in Iceland I was told that tarred/paved roads are a relatively recent thing, given the volcanic landscape and the large number of fissures and caves, it's easy to see how you could wonder away from the "road", stumble, fall or just try to find shelter somewhere and succumb to the cold.
I live in Iceland now, and while paved roads were not all that common at the time, it's not like they were barely-visible paths through the lava fields either.
But yes, in the area the article is talking about, the ground is a patchwork of these fissures, which could easily conceal a body. On the other hand, there would be almost no way to wander all that far from the road without knowing it.
It's not impossible that he would have died of exposure and never been found, but I don't think it's all that likely.
I'd agree that it's silly to assume it to the point of excluding all other possibilities, but would also think it reasonable to think foul play was a likely factor when someone heads home from the pub and is never heard from again.
When I was in Iceland I was told that tarred/paved roads are a relatively recent thing, given the volcanic landscape and the large number of fissures and caves, it's easy to see how you could wonder away from the "road", stumble, fall or just try to find shelter somewhere and succumb to the cold.