JKSManga
I figure Leo is safe until he teaches Quinn the 3rd stage of Qi and how to increase his Qi by absorbing it from the environment. Otherwise, there would be no point of him having figured it out on his own. Thereafter, he may have to sacrifice himself to save Erin and to allow Quinn to reach his full potential... but I hope not.
I'm curious as to if Quinns battle will require help and if he ends up calling Leo back, which would leave Erin alone. Leo and Quinn would both be upset about that, and Erin would fall in the hands of Pure. (or the dalki if they win but I dont know about that). Though, Im assuming Quinn knows Leo is with Erin, and wouldnt separate them lightly.