Definitely doable without a warlock. We killed it a few hours ago without one and it was okay.

Dunno the exact cooldown but we always get 2 Tornado phases (and our DPS is pretty decent).

What you have to keep in mind is:

- The healing debuff only applies to those CASTING inside the tornado area, meaning anyone outside can heal those still in without any problems;
- Don't start running as soon as you can. Wait a second or two, be mindful of the path of the tornadoes and don't be afraid to turn back a bit to wait for a tornado to pass by;
- They move in a circular motion around the room so you can easily predict their path, just hover your camera from above and don't panic;
- Define a stacking point (the circular pattern on the ground just outside the tornadoes is good) for people to stack and drop heals on;
- Make sure everyone uses defensive cooldowns. From a Paladin's perspective, Devotion Aura is pretty good here and so is unglyphed Divine Protection;