Leaving the faith means becoming inactive.
I believe that "leaving the faith" is the same as "leaving Jehovah's Witnesses". If this is the case, then I would say that becoming inactive is merely one way (of only 2 options I can think of) of leaving Jehovah's Witnesses. Another option to leave Jehovah's Witnesses is to disassociate oneself. It's an option that has been discussed many times on this board.
It's really a matter of semantics, but I honestly believe that becoming inactive is not the only way to 'leave the faith' of JW's.
DAing yourself is disfellowshipping yourself
The final result is the same, you get the cold shoulder. The means is not, though. When someone is DA'ed, no JC meets, no 'sin' is required. I disagree with, but understand, the WT reasons of DF'ing and treating them the way they do. What basis do they have for treating DA'ed ones the same way? I see no Bible support whatsoever...