I decided to email the race director and just see what the deal was with bowing out of the Montana Marathon, and great news! I can pass my slot on to someone else or defer my entry to next year (at which time I would probably try again to sell it to someone else, because I can't see wanting to do a marathon three months after the Ironman). Maybe if I can defer it twice, I'll do it in 2012.
I think I love how casual these Montana races are. When I asked how long I had to decide whether I wanted to defer, the answer was, "Uhh, whenever. Just let us know sometime before the morning of the race." :)
So that's a load off my mind. Unless I have a running epiphany when I get back from our trip, the marathon is off. I will bike, bike, bike, yoga, and swim. And finally go get some PT for my hip, because I've just been living with the same pain for like two years now, and that can't be a good thing.