No I would not leave if there was no myshop if ever that were to exist. But right now I'm fine with it because it seems to be a necessary evil.
I totally agree with Shirakani. You can choose MyShop or monthly sub. Though there are benefits with monthly subs...other games like WoW have fantastic ingame content, and new stuff arriving fairly frequently (though most of it is skewed towards lvl80+ers which I am not) but despite being one of the cheapest p2p, I can only afford to play it for, literally, 4 months a year. That's a whole $60! I don't have a job (for the next few months at least) and being in college, I cannot spend money on stuff like that.
I LOVE Trickster, it is out of the hundreds of MMO, one of the only two that hold my attention. If it were to go P2P I'd sadly have to quit and leave all my hard work behind.
I'm not defending the items in MyShop (not like I haven't bought pets from it though), a lot of them are ridiculous. I think they really should have more ingame items that are worth something, but ah well. What are you going to do? Have myshop, pay sub, or have no game at all?