I figured it out.
IMPORTANT: under all circumstances do not delete iCloud calendars. You'd think intuitively that the data is backed up on the cloud but sorry that ain't so.
You CAN recover the data if you have an archive or if you keep iCal on another machine (or apparently iPad though a more complex process that Support would have to help you with) from syncing (i.e. DO NOT open iCal with any kind of internet connection). You have to Export each separate calendar to a file and once you have done so, connect to the net (and watch your calendars magically disappear). The Import each of the calendar files to iCloud and life is good again.
If there are no backups, and all machines are synced, you're SOL.