If it's a full on getting back together I think that should only happen once if at all. Unless there have been some major changes most likely another breakup will take place. Truthfully once you've given your all to a relationship there is nothing new to contribute.
Getting back with someone soley based upon their appearance falls more into the "booty call" or "friends with benefits" catagory in my mind. In the end we are who we are. If nothing has changed on the inside then whatever lead to the breakup is still there.