Well, he's pretty far away from Alistair still at that point! I just see nothing in the scene to indicate that Sam has looked for Dean. He hasn't gone there expecting Dean to be physically injured. He's gone there angry that Dean was taken for this task and wanting to do it for him, all his focus is on Alistair.

LOL we're both too sleepy to debate properly! I wrote notes on 418 before work but can't bring myself to even think about those notes now. Need rest. Doing actual work might provide that rest...*G*