The "bad news" is that even though you might have multiple sclerosis, you still need to worry about all the other health and aging problems like heart disease, cancer and stroke. In fact, if your multiple sclerosis limits your ability to exercise, your risk for some of these other diseases may increase (in this case, multiple sclerosis symptoms may contribute to, but not cause, death). In other words, you still have to exercise and eat right just like everybody else.
In particularly aggressive, rare forms of multiple sclerosis, doctors may determine the MS was the cause of death. This was much more common years ago when multiple sclerosis treatments did not exist and there was not adequate medications and therapies for symptom management.
In fact, life expectancy of people with multiple sclerosis is nearly identical to the life expectancy of everyone else - almost 80 years in the U.S. So take care of yourself and learn to live as best you can with multiple sclerosis because you'll be dealing with it for a (hopefully) long, long time.