Awesome, your method allowed me to figure out another way that this can possibly be done(it worked for me, i was a bit mad at myself considering i usually back up my saves in case this happens, but then get burned on the one i wasn't backing up regularly, grrrr). I backed up my files before trying just in case, but if you create a new world with the same exact name(I used same seed also just in case) as the one that isn't showing up, it appears to use the same folder and previous data, but fixes whatever is broken. I also had mods installed, which may affect the outcome, not sure. It worked for me with Minecraft 1.6.4 with the Attack of the B-Team modpack installed. Although, I'm guessing that the way it loads a level save is fairly similar to any other regular minecraft save, so it will probably work with other minecraft saves that disappear from the launcher due to something becoming corrupt in the level files.