If you are in within 25 yards youll get the debuff that will kill you, the trick is to always be 25+ yards away and you will never ever get that debuff. Takes some doin both from tanks and dps but its quite easy if your just aware of it.
This is simply not true. I play a sorc hybrid build using affliction and crushing darkness. I kept getting the fearful debuff at 30+ meters. We started thinking it has something to do with dots. So when the right mob gets to 92%, 72%, 52%, etc I stopped dotting. Didn't get the debuff after that at 28+ meters. We we're also thinking that it may not be the distance from the boss you are dps'ing, but maybe where the other one lands. Either way, I am 100% sure you can still be hit with fearful at 25+ meters, just not 100% sure why. I completely stopped dps'ing and stepped back to test it, a couple of times.