Over longer periods of time, the crawl will continue to drop in temp as cold air from outside and inside flows down to the lowest point. Odds are your pipes wont freeze but every house is unique. Same way a small light bulb can add heat to a small space, a small lantern or two can add heat and light to your crawl. You could insulate your pipes wherever they run then funnel your heat source towards the air gaps that have the pipes in them.Mostly just wondering that if I were to only try and keep say the main living area warm for the family, I could close off all the bedrooms, which would mean closing off the master bath as well. Would only heating that space allow enough heat to leak into the crawl space to keep it above freezing?
If no power means no plumbing, drain the pipes.
The most interesting thing I have seen in the last 15 years is wood pellets. I am not using it as my primary heat source but we are only burning pellets in the fireplace this year, and it was built in 1950 so its not the most efficient thing. For the size room it is in, it has a lot of mass. It also has custom steel doors so it acts somewhat like it has an insert. With the wood pellet basket in it and good control of air flow we have been very happy with it so far.