If you've tried going through the entire list of fixes, Repairing permissions, Rebuilding Thumbnails, Repairing Database and Rebuilding Database and none of them fixed it, I would try them each again. I know it sounds crazy, but if they each do something different, it's possible fixing one later down the line will do something that will now make one of the earlier steps “work” now.
If you've already tried each step multiple times, and you are still having issues, if I were you, I would go to the next best option and that is try a third party application called “iPhoto Library Manager” by Fatcat software. I hear their software really works well to rebuild and repair iPhoto libraries.
What's unique about their software is that it doesn't just try and do the same thing iPhoto's First Aid does, it actually constructs from the ground up, a NEW iPhoto library file using your original one, taking pieces at a time to build it until it's “remanufactured” a new and improved one.
Here's a link to their software: Fat Cat iPhoto Library Manager
Ripping your photos out of your master's folder in the package contents and then re-importing them is an option, but I would ONLY consider this a last resort.
First, if you have edits on these photos (color corrections, crops etc) or you have added captions or new names for each photo, reimporting them will cause this information to be lost. It will be like you are starting over again with brand new photos.
Second, what if after you've re-imported these photos you update iPhoto someday, or something causes your library file down the line to “repair” itself, and all of your old versions of these photos come back “online” again. Now you will have duplicate copies of all of your images that you will have to deal with. In some situations, this may not be a problem. For others, with lots of events and photos missing, trying to figure out which version to delete could be a massive headache.
I understand the emotional need to get ALL of your photos back as soon as possible. So, do what you have to feel better and move on with your life. I'm just suggesting to try and do all of the steps you can to fix your current situation without declaring a “photo bankruptcy” and re-import all of your missing photos. It could just save you a lot of headache in the long run. ;-)