Well, if he's not bringing Fire Dragons in Wave Serpents, your Knights are pretty much in the clear. I guess the Warp Spiders could put on a few glances, or Wraithknights striking before you, but...2 Avatars
2 Farseers on Jetbike
10 Warp Spiders
3 Wraith Lords
2 Wraith Knights
Thunderfire Cannons are your friend for clearing our Zombies, I think. Slow and Purposeful might even be more crippled by the burrowing rounds that trap them in difficult terrain!
Tigurius with Scrier's Gaze + Stormtalon should be able to put some hurt on Heldrakes--making sure to come in after the Heldrakes come on, zipping around to deal damage in rear arc AV10 if possible...