6 682 500 unmitigated
-30% vigilance (use at t = -2 to 0 and t = 8 to 10)
-30% hand of sacrifice (use at t = -2 to 0 and t = 8 to 10)
-25% defensive stance
-10% weakened blows
-10% demoralizing banner (use at t = -2 and t = 5 to 10)

t = 0 use:
-45% rooks unlucky talisman (15sec)
-40% pain suppression (8sec)
-20% demoralizing shout (10sec)

t = 8 use:
-40% shield wall

and for blood rage (2) at t = 8 use:
-25% power word: barrier

damage taken (per hit during a period of time (seconds)):
t = 0 to 8 = 525 152
t = 8 to 10 = 315 091
t = 10 to 15 = 393 864
t = 15 to 20 = 716 116

assuming bonus attak power from vengeance caps at unbuffed hp (~980k), a point i'll get to after 9 or 10 hits (~15sec in) a full shield barrier will absorb: 3(0.6*AP - 2*STR) ~ 3(0.6*(50000+980000)-2*27500) = 1.689m.

I'll have 120 rage and 0 stacks of debuff when the phase starts.  Last stand to last through-out so aprox 1.3mil max hp. 1 full shield barrier should absorb about 160k, Power Word: Shield will be used before the 1st hit so that should block out most of the damage.  I will also have enraged regen to restore 20% of max hp instantly and another 20% over 5seconds which will help out.

I'll use another shield barrier after the 2nd hit, about 350k dmg in size and by the 3rd or 4th hit i'll be back at 120 rage.  I'll use another shield barrier after 4th hit and then after 6th hit (this one should give over 500k barrier).

By the time t = 13-15, i should have at least 60 rage and this will give me a shield barrier for around 1.5m. this should last for 2 hits and then the remaining hits i will use any rage i have left (20 rage barrier only gives 500k).

I'm guessing there shouldn't be more than 200k hps needed until t=15, in which case there will be a few seconds where no healing is needed (huge shield barrier) and then a couple seconds where it may get pretty crazy.  this has been a pretty conservative estimate of rage so i can see some extra 20 rage barriers happening near the end, especially with sword and board procs.

also, i could test out warrior 4set as if i demo shout at t=10, the last 10seconds i will be gaining rage per hit.  i am not sure how much rage i would get but even 10-15 per hit would suffice in getting some extra shield barriers in.  need to find maths on this/test it out because no where else does a 4 set really matter.

all in all, if CDs are used properly at the start, there should be a few seconds where healers have time to boost the HP up.  in the middle it should be pretty smooth, hp hopefully never below 75%, and the last 5 sec could have 1 or 2 big spikes, but with 4 set and some shield slam resets, there is a good chance there may not be any spikes of damage at all.

2nd time round 25% more damage = shield barriers get higher quicker and in general there shouldn't be much of a problem until the last 5 seconds where shield barrier will be reduced quicker, but there still shouldnt be more than 2 spikes of damage in a row, thus i should be able to survive (even if not 100%).