The Icelandic authorities are pulling out all the stops to, basically, recover the body, but the locals have a much more practical viewpoint.
They say that It is unlikely that the man has drifted out to sea. Lower down the river, it spreads out into sand bars where most things that fall in show up eventually, according to farmers in the area.
Uh, his fate is he drowned in the boiling torrent, geniuses. His corpse is stuck in a crevice or rocky spot, and unless the water goes down, his bones will stay there. Or, he'll wash up on the sandbars downstream. Just watch for circling seagulls, and you'll know where he ended up.