The ‘Sync’ option is set to equalize your iPod to your iTunes. If the songs are no longer in iTunes, then when iTunes syncs the iPod, it will erase the songs from the iPod, not put them back into iTunes.
You might be able to connect your iPod and then catch the process when it starts and cancel the sync process. If that works and your iPod is still connected to your iTunes, you should be able to access the properties of the iPod and choose ‘Manually Manage Music.’ Then you can connect you iPod to this iTunes or other computer/iTunes and not have it try to delete everything.
You might also try connecting this iPod to another computer and watch for the ‘Erase and Sync’ prompt. You can say ‘No’ and then use that iTunes to change the iPod’s settings to ‘Manually Manage Music.’ Then when you connect it to your iTunes, the ‘Manually Manage Music’ option should be applied there too and it shouldn’t erase the iPod.
As far as getting your music back into your iTunes, a Google search should give you hundreds of solutions. Media Monkey is one of them.
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