It is difficult to pin down LFR as being the cause of the subscription loss. Time has passed, plus a lot about the game has changed (from talents, to theme, to how classes play)... any one of these can be the cause of subscriber loss. Unless you have hard data, i.e. a departing player saying "LFR is why I quit" then it's entirely subjective.
Anecdotal "data": Many of my guildmates left WoW in Cata to play SWTOR for a change of pace. Few have returned to WoW. Fewer still have stayed with SWTOR -- altogether, they've simply moved on to other things. None of this was caused by LFR.