Well glad it worked for you, but last time I asked I was told it only worked on sarcoptic mange and not on demodex which, although caused by a mite, is an auto-immune problem, thence the reason why the animal should not be bred from. However this was a couple of years ago and it could be that Stronghold has been changed so it would be well worth asking the manufactures for their opinion. Also the vet as the application of chemicals to a dog already suffering with a reduced immunity may not be advisable.
The Demodex canis is present in all dogs, part of the canine natural inhabitancy. When the dogs immunity falls for any reason, be it illness, or some other cause, the dogs immune system is unable to keep pace with the mite and it then reproduces in vast numbers under the skin and damages or inhibits the hair follicles. Killing the mite with an insecticide cures the signs of an overgrowth of the mite but does not clear the dog of the mites altogether, so although the hair may re-grow the dog is not cured. However once your dog has suffered you can be on the lookout for another attack and deal with the problem early.
Edit: Stronghold product information
here will continue to look and see if I can find anything with regard to Demodex