Hard to say, since it's not clear what his position is on Afghanistan. Sometimes he sounds sensible and makes noises about building at home, not abroad. I suppose it's not a good thing that even one of his supporters doesn't know his position on this, but then again, that is how Obama got elected (by being vague).
A rather strange question. I'll just say that I hope the number is zero and leave the prediction of US deaths to others. But to the policy issues...I don't think there would be a huge difference between how Obama and Romney approach Afghanistan. If I remember correctly, Obama has promised to have us out by 2015. Because of his base, he feels compelled to make such promises, but I think he's just as likely to draw down our presence there as Romney is. Campaign rhetoric aside, I think they're both pragmatists on foreign policy and the use of force overseas. Still, I wouldn't be surprised if Romney criticizes Obama for wasting US lives on a fruitless policy. There is ongoing war-weariness in the country and that makes this a viable issue for Romney.
Perhaps the supposition is that Obama campaigned rather vaguely, but definitely transmitted that he'd like to leave Iraq while concentrating on Afghanistan, and then leave Afghanistan. Romney transmits that he'd like to be more aggressive everywhere, but that's obviously impossible in a troops-kind-of-way and he's positionless in general. So I'm guessing deaths would go up again for a year or two, and then he'd do just like Obama would, and leave, but after more deaths. Vaguely like how healthcare will eventually "play" out. Yay. Progress.
Who are likely to be Romney's picks for cabinet positions and advisors related to defense/state? That seems an important point. Which factions of the GOP are represented in his campaign's current military/foreign policy advisors? That's probably answerable right now, but I haven't looked.
At The Washington Post
At The American Prospect