[Lizard]

Cratner, there's a small chance of recovering this data if you have a Mac that also syncs with your iCloud calendar and a backup system like Time Machine.

If that's true, you could find the folder iCal stores its files in and use your backups to look for any files that might have been deleted in the right time frame. Even this is a slim chance because it would require the Mac to sync with iCloud and make a backup before OmniFocus tried to capture the reminder.