The heal is not really all that much, iirc like 225k, the point is to burn him in 1 min 30 seconds (with 3 dks 1 min flat with 2) which is very feasible with 9 possibly 9.5 well geared dps. You will get at least one heal, but your going to basically have to just burn through it.
EDIT: I was looking at the 25 version of engulfing shadows. He should only cast this heal on any that get low, and since your straight burning yogg himself that should be a non issue. But even if he chain casts it thats only 2 heals or having to burn a total of about 3.5 million damage. If you go with 9 dps each will have to do at least 4.5k dps as a bare minimum to get the burn done. That number is a rough estimate but even so these numbers are extremely attainable, the only real question that arises is will one army of the dead last the 30 seconds, specifically near the end.
Really this is all an idea, nothing more. No way this is the intended way of doing the fight, kind of like the recent freya 3 burn video where they just dpsed her down at full stacks. (
http://www.youtube.com/watch?v=PuvKiJsG ... r_embedded for those curious)