Melissa--
Sandy Headwall is a less-traveled route on the west side of hood that some ski/board down after ascending. A fall here can result in a long slide. Iain can offer some insights into this.
The scenario you describe involving the stuck snowboarders is similar to what happened with a group of students from the Oregon Episcopal School back in the 80s (I may have the date wrong). One of the worst "accidents" on hood ever.
You could have your snowboarders leaving the top of the Palmer and booting over towards Illumination rock for a long ride down, get socked in by poor visibility and go for it anyway (no compass or GPS), only to make the fatal flaw of following the fall line down over the Mississippi headwall. This, in fact, does happen on Hood.
Good luck!