It depends on how torn it is. The aorta
has three layers of linings, and sometimes, a "torn aorta" involves only one of the layers. This actually recently happened to a friend of mine, which is the only reason I know...he had the two internal layers rupture all the way from his chest to his groin. For him, the treatment is to keep his blood pressure down, and allow the tears to heal themselves, and for the body to absorb the blood that got in between the layers.
Another option would have been surgery. For surgeries that involve the heart and major arteries, the doctors will usually stop the heart. They will do a temporary 'bridge' that connects to a machine, so that blood can continue pumping through the rest of the body. Depending on the size of the tear, it could be quick, or it could take a couple of hours.
Generally, the aorta heals itself pretty well. One of the things that's important in healing is blood flow...and since the aorta is full of blood, it usually heals up pretty quickly. This is why bypasses are so often successful.
If he is at the point where the doctors have diagnosed it, he's probably going to be just fine. Just make sure he does exactly what the doctors say, and he's likely to be completely healed in a month or so.