To me: If it dies at the 2nd burn phase and everyone is not stressed out of their skulls and still alive, its all good ;-)
Then we proceed with vendoring the hunter/warrior/shaman token and disenchanting the mail loot /facepalm
I also don't think reforging mastery is the way to go. The GCD cap is only limiting our mind flay damage, Dots will be ticking super fast, AND the haste is multiplicative. So you would be triple dipping, DI + hero + 25 stacks!
Flay all the way, sear would overcome the gcd cap issue on flay but I doubt it outweighs the shadow orb generation and permanent fiend that flay provides - remember that your orb generation from pain isn't really altered - so you depend on flay for big MB's and ES.I could still see an argument where you would want to switch to Sear if you had 3 orbs inside an MB cooldown and your fiend cooldown was back up but your fiend was still alive - then swap to sear - but that seems somewhat unlikely (I will watch for it though next week).