I wouldn't even say there's a need to specifically step down from being an MS. Just keep refusing responsibilties/talks due to 'other commitments', start missing meetings and they'll remove you.
There's a lot of talk on here about people being DF'd for not going anymore but it only happens when they open their mouths. It really is a case of loose lips sink ships.
I stopped going over twenty years ago now; I didn't get DF'd, my wife didn't get DF'd, about 80% of those I grew up with have stopped going now and I can only think of one that got DF'd.
Saying that, I don't know of anyone that got DF'd for apostasy 20 years ago; now I would imagine it's probably the most common cause.