Found a selution. Final cut pro makes the backupfiles in the ‘movie’ folder where you can find the backups. If you open with rightclick and open content packages find the event you are trying to save and copy the ‘CurrentVersion.flexolibrary’ file and replace this file in your current folder. This makes the event visible again. Hope this helps.. make sure you don’t overwrite anything and back up your folders..
I found it on the apple site: https://discussions.apple.com/message/25598846#25598846
Did you find a better answer to this problem jet? Im having the same issue here, and there must be a way to fix this instead of going back with time machine?