Well, as a veteran and eccentric Skaven general I may eb able to help you...
I would tend to say you need two things: a mage and a unit of archers. Both fit perfectly into any respectable High Elf army, without tailoring it to your opponent (something I strongly oppose).
Ratlings are not what they used to be... They can, with the 7th. Ed rules, always be targeted, even when close to an allied unit! A single round of shooting, or magical bolt (whatever domain you are using) should easily deal with it.
As for the Warp-Lightning, try to cast Drain Magic, since you get the spell for free. I can't remember if you need to take High Magic in order to get it, or not... It will raise the casting value of the spell to high levels and thus greatly reduce the number of hits you will take.
A Lion chariot should then be able to strike at the weakened Warlock, despatching him for good.