WolfL,

I think that you're finding that a lot of hot / cold isn't helping. (or, it may be that the rsd is simply progressing).
Sometimes, the rsd feels better in warmer temps, because as I just explained in another post, how humidity, or lack of it, can effect the pores. (rsd seems to have an effect on all kinds of things that should be automatic, now they're not. Like, if you get a chill, you may perspire.) Stimulate the sympathetics, and, more often than not, something bad will happen. (Or, probably not what you'd expect, normally).

If it's only your foot, that you need to keep warm at night, maybe a loose, but warm sock would help.
Electric heating pad.
As far as electric blankets go, I FAR prefer the ones that cover the mattress, rather than cover me. Why? Because as we sleep, and we get too warm, we can toss the blanket off.
If it's a mattress cover "automatic" (like a Sunbeam), you usually set it and forget it.
Even if you toss the blanket, or, it falls off, you're still warm! Amazing difference!

I'd say not to play around to much with the temperature changes on the foot, because this whole thing is about NOT stimulating the nerves, they're over active already, and don't know what to do, when stimulated.
A luke warm epsom salt soak would be good.

If your foot gets cold, does it also get clammy and wet? (Cold sweating)
My feet do, (i'm full body), and I spray my feet with anti perspirant.

As far as your last question, will the major pain come, I'd love to say no. All I can say is I doubt anyone knows.

Like Bobber said. Prayer is good!

Be well,

Pete