Well, I've managed to get reception back, but only by jury-rigging a solution. It seems that the dish itself remained fixed (i.e. all of the various alignment screws are clearly still in the position they were tightened into when it was installed), but the wind on the dish wrenched the board it's attached to slightly out of line, so that the whole dish is pointed slightly lower than before. I tried to correct by raising the elevation a bit with no luck. So, for now, I've restored signal by bracing the dish back into position with a board run to a fence a couple feet away, but I think that it needs to be remounted in order to really fix the problem.
So the Dish Network guy is coming out on Tuesday and I've got a work-around in the meantime. Thanks for all the help and advice.