Well, the WW Game Day at my store didn't go as planned at all! The second DM who was supposed to show up has fallen ill, over half of the people who said they would be there didn't show up because;
a.) "my brakes on my car fell apart so me and so-and-so can't come" (email comlete with pictures of said exploded brake pads;
b.) I couldn't get off from work;
c.) I didn't hear my alarm go off;
d.) (Haven't heard from them yet)
Nevertheless, those who did show up waited patiently while I whipped up a small adventure using the materials provided and it turned out to be lots of fun!
A few questions did arise in my mind however;
The next time a WW Game Day happens and disaster strikes which prevents any other RPGA DMs from making it to the event, can I allow another player to DM a table even though he/she isn't a WPN Organizer or DM?
If I report a player as having DM'd a table, will there be consequences, and what are they?
Does a low turnout of people (6) at my WW Game Day event affect my future WW events as far as WotC is concerned?
Ironically, I had four more people show up later in the evening (after the event) who wanted to play D&D, and had 8 people show up to play the next day! Go figure...
can I allow another player to DM a table even though he/she isn't a WPN Organizer or DM?
The only requirement of any DM, in any situation, is a valid RPGA/DCI number. You have never had to have any other rank or qualification in order to DM.
There have been various different qualifications required to order and report adventures, but never just to DM.
I assumed as much, but wanted to be sure. I am wrong far too often! 
Thanks for the quick reply!
You might consider a pre-pay to register set-up through Warhorn if cancelling players become an issue. Many gamers can be pretty frugal and would put in the extra effort to make it before they'd waste their adventure fee. Might not work in all situations but, can be very good when you have more players than seats at games.
Thanks, MatteBlack! That sounds like a good idea. The only problem is that about half of my regular players seem to be on the poor side and might not return if we start charging to play. Right now it's free. Maybe a "Pay for a guaranteed seat" option would work. I just don't want to give the impression that the D&D experience in my store is all about money.
What about a "pay to sign up, get reimbursed when you show up" scheme that only makes the people who flake out have to actually pay permanently. :P
Take the collected fees and put them towards gift certificate to the DM for their services and it will probably help you on both ends. There are always those who will grouse about having to pay anything but, as long as people see them money going back into making their gaming happen most people aren't going to cry over a few bucks.
The problem with free is it is often interpreted as 'low value'. The problem with fee is that it often creates a pressure on the gamer not to sign up. I would rather hold gamers accountable and increase the way they view the value than to scare them away with money issues. There are a lot of poor gamers.
You might consider a signup to require phone and e-mail. Two days before the event, send a reminder with time, date, address, plus a bit about how important it is that they show up or give you warning ahead of time.
Then, on the day, if people don't show, call them.
That is likely to create a bit more responsibility on their end, as they understand it matters.