Assignment

Chris, I "feel your pain"! But, I don't have a fix, other than to suggest that maybe
your admin has a weekly backup of the course that could be restored? It would be tricky if the course had evolved in the interim!

I did report this problem at http://moodle.org/mod/forum/discuss.php?d=44761
as "Calendar event deletion deletes object instead of reference". Perhaps we should instead create a bug report, and reference these two discussions?