Sorry that you are having this trouble. Best of luck with this issue. I would assume that your client keeps backups of its data, so while the situation may be embarrassing it may not be as bad as you think. You might look into getting a better backup system for your work, because data loss does happen occasionally with any digital system.
If you keep a Time Machine backup it might have a backup of your library in it. You can access your projects by restoring the library to a date before you lost the projects. If you restore the library, restore it to a different location than your two current libraries so that you don't overwrite them in case you need to use data recovery software. Be aware that if you open, or have opened, and older library with a newer iMovie app the library will get updated and you won't be able to open it with the older iMovie version.
You might look into data recovery software. If you use such software you should do it quickly before the lost data gets overwritten. Here's a link that lists some software recovery options:
https://www.cleverfiles.com/howto/top-5-data-recovery-software-mac.html
I've not used any of the recovery software mentioned in the above link, so can't vouch for them.
Also, before doing anything more you might benefit from talking with the techs at Apple Support, who have the capability of remotely accessing your computer, that we cannot do here. To contact Support click on the Contact Support item in the upper right hand corner of this forum's screen and navigate to a place where you can enter your phone number.
Again, best of luck with this.
-- Rich