The progressive time line will vary from one person to another. If you are dillegent about avoiding triggers and maintaining a program of exercise, stretching, and sound nutrition, you may be able to off-set the curve. I am still walking, though with a cane. I had a good 20 year run, but it has caught up with me. I will not relinquish my independence, though, because I have too much yet to do.
Your doctor might be able to get you some case study results, but you will find that there is no case that is representative for all. Additionlly, symptoms can vary. My neurologist told me that she looks at a 3 year picture. That is, she told me that the symptoms I experienced over the course of three years will be the symptoms I will most likely have to deal with from now until the end. Progressive means that you will deal daily with problems without any rest periods. It is like playing a full game of football (or Aussie rules football) without any rest periods.