*If I attempt to sync with itunes now, will it delete any songs in the ipod that are no longer showing in the itunes library/list?*
Yes it will.
*I would like to add a few new downloads from time to time but dont want to risk losing the existing contents of my ipod...? (Is there a command to prevent itunes deleting songs in my ipod?).*
If you simply want to continue using the iPod without syncing (and losing the contents) then change it to manual management. Open iTunes first and go to Edit>Preferences>Devices and check the box "Prevent iPods and iPhones from syncing automatically" and choose Ok. Then connect your iPod.
Alternatively you can use a keyboard command to prevent your iPod auto-syncing with iTunes. While connecting the iPod to the computer on Windows with iTunes installed hold down the Shift + Ctrl keys together. This will stop the iPod from auto-syncing with iTunes and the iPod will appear in the source list. Wait until you are sure the iPod has mounted, and that it will not auto sync and then you can let the keys go. This may take between 20 to 30 seconds depending on your computer:
iTunes - Keyboard Shortcuts for Windows
When your iPod appears in the iTunes source list check the "manually manage music and videos" box in Summary then press the Apply button. In manual mode you can drag and drop new content to the iPod from iTunes without erasing what's currently on it:
Managing content manually on iPod and iPhone
If you want to recover the music from the iPod and transfer it back to your computer there are a few things you can do. iTunes will only give you the option to copy your iTunes Store purchases directly from an iPod to the computer, you'll find details in this article:
Copying iTunes Store purchases from your iPod or iPhone to a computer
For everything else (music from CDs, other downloads etc) there are a number of third party utilities that you can use to retrieve the music files and playlists from your iPod. You'll find that they have varying degrees of functionality and some will transfer movies, videos, photos, podcasts and games as well. You can read reviews and comparisons of some of them here:
iTunes & iPod software
Wired News - Rescue Your Stranded Tunes
Comparison of iPod managers
A selection of iPod to iTunes utilities:
TuneJack Windows Only (iPhone and iPod Touch compatible)
SharePod Windows Only (iPhone and iPod Touch compatible)
iPod2PC Windows Only
iDump Windows Only
YamiPod Mac and Windows
iPod Music Liberator Mac & Windows
Floola Mac & Windows
iPodRip Mac & Windows (iPhone and iPod Touch compatible)
iPod Music Liberator Mac & Windows (iPhone and iPod Touch compatible)
Music Rescue Mac & Windows (iPhone and iPod Touch compatible)
iGadget Mac & Windows (iPhone and iPod Touch compatible)
iRepo Mac & Windows (iPhone and iPod Touch compatible)
iPod Access Mac & Windows (iPhone and iPod Touch compatible)
TouchCopy Mac & Windows (iPhone and iPod Touch compatible)
There's also a manual method of copying songs from your iPod to a Mac or PC. The procedure is a bit involved and won't recover playlists but if you're interested it's available on page 2 at this link:
Copying Content from your iPod to your Computer - The Definitive Guide
Once you have recovered everything from the iPod and your iTunes library has been rebuilt it will be safe to sync again.
I would also advise that you get yourself an external hard drive and back your stuff up, relying on an iPod as your sole backup is not a good idea and external drives are comparatively inexpensive these days, you can get loads of storage for a reasonable outlay:
Back up your iTunes library by copying to an external hard drive
