I can empathize with Jim on this issue. If I get to the point of SPMS I'll stop the meds too because at that point they don't really have much evidence of working since they're mostly for relapses. I haven't had a relapse in more than five years so I might actually be there too, but I have my head in the sand and I'm still working, and say my prayers all the time that I can continure.
Jim is awesome and I hope this will improve his qol. I know if I need to retire either voluntarily or not, I'll likely stop with the Nuvigil since that is the med that keeps me working.
God bless him and you too for all you do for the rest of us with your wonderful examples.