if you dont have any save in any of the mod packs then you have nothing to worry about loosing
as for the redownloading problem, idk it works everytime usually
If your on windows its under "'name'/appdata/roaming/.techniclauncher"
open up you mod pack of choice and copy out the save file
Not sure if its the same with mac
copy all your saves onto your desktop, then deleate the technic launcher in its folder and recycling bin then redownload it, then copy your saves back in. I had that problem at first, but that works a charm