I'm assuming the % missing health maxes out at 30%... I think this is standard but I can be incorrect.
Assuming ~300 HP ranged caster minion (assuming maxing W first). I'm also going to assume just a base Doran's Ring (or spellthief's edge, it's not much difference in dmg). It's 42 damage per second with a base 230 damage rank 3. I'm also going to assume every 7% max HP is an increase of 17% damage of the ability.
(also I know it's done in half ticks and not full second ticks, but I'm lazy so the actual damage is going to be higher)
first tick takes them to 258 (which is 86% hp so 34% more damage next time or 57 damage)
201 hp left (67% max hp so ~80-85% more damage so i'm assuming 80 or 76 damage)
125 hp left, then at this rate, they'll die even with 76 damage per second since it's 2 seconds left.
I think it'll still wave clear.