i would spec it shadow until mindflay. if you want mana regen too.. then vampiric embrace/touch (forgot which one) is nice. i forgot to mention the spriest does have two Dots to add, which is swain and devouring plague. mindflay to slow your feared mob down so you dont have to run after them after the first drainlife, as i've encountered this before. your sprist's renew will probably be enough to keep the warlock happy. i'd spec to improve renews, improve fortitude and mindflay. the rest is up to you to decide.