Brake Light On problems of the 2015 Cadillac Escalade

At 15000 miles and original owner while towing our brakes completely gave out. No warning sign, no leakage, only 1 symptom a few months prior where the brake peddle was mushy. Dealership said it was fine. Everything worked fine driving it throughout day. Stopped for dinner just before we entered mountain pass. Got in SUV to leave for home and had no brakes at all. Emergency brake won't even kick in to be used for emergencies. The vehicle gave no warning signs, engine or brake light warnings. No changes in brake pressure, no leaks under vehicle or on engine. It was an instant give out of brakes and could have happened while driving. Fortunately they did not give out while moving more than 3 mph so we are still alive. Dealership and gm both said it was normal for brakes to give out and not have any brakes when the brake master cylinder gives out. This is not normal! they replaced the master cylinder and all works fine now. However I feel this is a major vehicle safety issue in that for a vehicle to completely lose all of it's braking ability but not be prewarned that there is a problem is extremely dangerous. If we didn't stop for dinner the brakes would have given out in the mountain pass and me and my family would more than likely be dead at the bottom of a mountain cliff! we are extremely afraid to drive this vehicle now and gm has no interest in buying it back or helping us get out of it. They just said "just wait to see if it happens again" which to me, means, wait until you cause a fatality. They also said this isn't happening to other gm vehicles.