I'm sorry that this happened and that a lot of work was for naught.
But maybe some good can come from it, by making it clear to newbies
that minimum turnout is required at contests. The contest invitations
I've seen have emphasized the maximum number of entrants, but I don't
recall seeing that a minimum number was required.

I have no suggestions on what to do about no shows. Emergencies do
happen, but I can't believe emergencies happened to 25% to 40% of the
people who sign up. Sounds like selfishness and rudeness to me.

-John