We know that a number of people with MS are never dx, and autopsy studies have shown that 8+% of the general population actually has MS upon death. That's a lot of people that don't ever progress . . . however, I'm assuming you mean those of us who are diagnosed and not benign.
Statistically, "After 10 years, 50% of people with relapsing/remitting MS will have developed secondary progressive [Weinshenker et al, 1989, Runmarker and Andersen, 1993, Minderhoud et al, 1988]. By 25 to 30 years, that figure will have risen to 90% [Ref]."
That doesn't sound very encouraging, but those statistics may be changing now since many of us have access to DMD's earlier in the game. That's the only stat I could find in my notes though . . .
I am not a Neurologist, Physician, Nurse, or Hairdresser ... but I have learned that it is not such a great idea to give oneself a haircut after three margaritas