No data should be lost when restoring an iPhone - not unless there is a problem with the iPhone's backup.
All iTunes content on the iPhone - all music, tones, movies, tv shows, audio and print books, and apps should be in your iTunes library on your computer.
All photos transferred from your computer via the iTunes sync process should remain on your computer.
Photos/videos in the iPhone's Camera Roll can and should be imported by your computer as with any other digital camera - especially before restoring an iPhone.
Contacts, calendar events, notes, and Safari bookmarks can be synced with supported applications on your computer.
Do you have iCloud? What iPhone isit, if you restore it and then when the screen comes up you can chose to restore via iCloud and the last time it synced, iCloud syncs automatically so you should have the data backed up. And even if it didn't sync last time it can't have been that long before that it synced. You'll at the least get back most of your data even if you can't restore via iCloud.
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IMPORTANT: you should be talking to Apple or a data recovery specialist.
If the os on your phone is intact and just in recovery mode (DFU) then there are utilities available to break out and it MAY be accessible. Here is a link to someone who documented getting out of DFU.
Proceed at your own risk, I still will reccomend talking to Apple or a specialist. What is above is the only thing I can think of.