Are you sure these files have been deleted from your HD? Are you sure they are not in the Library Package?
If you think that this is a problem with iPhoto 11 then you're going to have to explain all the people who updated their Libraries and didn't lose photos. Frankly this is rather more likely to be corruption in your existing Library rather than anything in iPhoto 11.
Also, I honestly cannot understand anyone who would update software without a back up on any computer, on any operating system, for any application. Having a back is basic computer usage. Apple Even build in a Back Up application to the OS to make it easy for you. Really, would you drive without a safety belt -even though you think there isn't the slightest chance of a crash?
Btw, looks like mostly RAW files (.NEF) was deleted and all videos, .mov and .avi
If the NEFs are removed then the jpeg Previews will still be there.
Regards
TD