Some wise advice above from people who've exited successfully!
When I began my fade a concerned elder approached me, when confronted I simply told him I was taking a sabbatical from meetings...but why..I'm just taking a sabbatical...end of conversation.
Be polite but firm, you haven't got to answer any questions at all as to your beliefs, if you want to be a little mischievous you could say you've reallocated the time spent at meeting to reading Russell and Rutherford's books to get a better understanding of the history of the organisation and you've found it really interesting, perhaps they would too!
So my advice is simply go off the radar, like any other club or association resignation is not necessary, you simply stop going or paying your dues.
Snapdragon