How to nerf Maw
... before inevitably gutting it in 6.8. Rip Fiora. In all seriousness, here's how:
Remove/nerf the spell vamp. Of the 3 passives that Maw has this one misses the mark conceptually. It's intended to encourage the user to keep DPSing but it's far too easy to kite back while spamming abilities. Granted, that's technically DPS but not the "haha, Lifeline proc'd, as long as I keep attacking with everything I have, you can't kill me (hopefully)!" DPS that Maw seems to represent.