I'm not sure a move to F2P would make me leave as it would really depend on how it was handled. I have played LoTRO after it went F2P and I've played GW2, which has no sub fee, and the issues I had with both are not really tied to the cash shop or the fact that they are not sub games.

Personally, I'd probably go if the game became all about PvP or hardcore grouping/raiding. That's not my kind of content so if it was all there was to do, I'd leave because I'm not going to spend my time/money on a game focused on content I don't enjoy.