If you have your iPod set to "Auto Update" it will erase the songs most likely. You have 2 options, you can email the music store and see if they will let you "Re Download". There not obligated to do so but may.
The second option is to use thrid party software to read your iPod and copy the songs back to your PC. Most 3rd party programs require the "Disk Mode" for iPod. If you have not turned this on you will have to hold down the shift and ctrl key, connect the iPod and AFTER you see the iPOd listed in iTunes let go of the buttons. This will stop iTUnes from auto updating the iPOd and (Maybe) erasing these songs.
Now you will rightclick the iPod in iTunes, select "iPod Options" and check "Enable Disk Usage". Go here to now find out how to copy from the iPod using thrid party software
http://www.ilounge.com/index.php/articles/comments/copying-music-from-ipod-to-co mputer/
