I know you can't go back in time, but here's some advice to avoid these situations in future...
1) Upgrade AFTER the event.
2) Always keep a backup WITH YOU.
Now, let's see about helping you get everything running again...
Which OS did you upgrade from? After you upgraded, did you reinstall drivers for the devices? Sometimes that's necessary, even if the driver is the same version as what was previously installed.
You say you tested it at home with no issues, was there any difference in connections or devices at the gig vs. home? Did you test it in the same mode (running a video, for example)?
The reason it restored an older database was when you rebooted, the database that was in use at the time was damaged - it grabbed one of the 3 backups which are created every time you open and close the software. So losing 6 months of music doesn't sound accurate, unless you selectively restored an old backup (zip).
I'd be happy to help you try and recover your data and get things working smoothly, just let me know the answers to the above - I understand you were in panic mode trying to get things running before the start of the event, but knowing some of the specifics may help understand exactly what happened to your database.