If you updated LimeWire & cannot find your Downloads
LW will not have deleted them, simply the new version changed locations, so you will have files in two locations most likely. (Only exception to this is if you used the LW program folder as a download location, then installing the update will have deleted them.)
Doing a simple computer search such as searching .mp3 or whichever file extension you normally download will show the various locations on your computer where such files exist. Try that also.