Tab 2 recovering data from hung device
Firstly, data on your SD card will not be erased. Then there's a chance, that your contacts are already backed up on Google's servers, so you don't loose them either.

I don't know if the app will help. Harddrives don't delete anything, they just stop indexing the files and then rewrite the sector with new files, but (I'm not 100% sure) I don't think you can do the same with SD memory.