It all depends on how bad and how big. If the mats got to the skin, and are over a large area, I suggest have a perfessional groomer cut him short. If they are not that large and not tight to the skin, hold each mat at the skin and brush it out peice by peice like you would a knot in a childs hair.
If the dog is used to the brushing, it shouldn't be a big deal. If not, then it is best just to have it cut short. Emergancy happen, and the dogs kinda get forgot about. We see it from time to time, and you just have to deal with a short dog sometimes.
What kind of coat does he/she have? My mom's dog is part Schnauzer and has a wirery (sp?) coat. He doesn't mat much and when he does, they are easy to brush out. I use a steel comb. My mom has RA so she can't brush him that often either.
I also think it would be a good idea to go to a groomer and ask for a short, easy maintenance clip.
If you are going to keep your schnauzer in a skirt as well as the leg furnishings you will need to stay on top of brushing, at least a couple of times a week. Try a slicker or pin brush and a fine tooth comb to work at mats. Always pinch the mat so as not to pull the dogs skin.
Some people completely shave them, leaving only the beard and eyebrows.
When asked what he would do if stranded on a deserted island with nothing but a cow in sight; "I would find out what the cow was eating and join him."