[Brian]

Sorry for the trouble! OmniFocus for Mac will automatically create backups for you. By default they're placed in the Documents folder, and you can roll back to one by selecting "Revert to Database Backup..." from the File menu.

Once you do that, select "Replace Server Database..." from the same menu - that'll push the data up to your sync server.

Finally, sync your other devices. They'll ask you which database you want to use; have them use the Server one.