The solution to the issue with getting randomly instakilled is actually killing the ghouls. I spent a lot of time figuring that one out myself. This is also mentioned in the OP iirc.I encountered two problems this week with the heroic lich king.
The first one was trying to switch my lockout from 11/12 10 man normal to heroic 25 man. I had just cleared 10 man and zoned out and was going to switch to heroic 25 while outside of the zone, but it wouldn't let me zone in. The solution to this was to zone in on 25 man normal and then switch to 25 heroic while inside.
The second problem was a bit more involving. After burning the lich king through the second transition and getting harvested, partially through the throne room phase I was getting killed instantly. I had a sneaking suspicion that this was being caused by the adds being up top, however after a few pulls I was able to narrow it down to the shambling horrors, rather than including the raging spirits. I decided I was going to have to kill the shambling horrors; my solution to the problem was unglyphing avenger's shield to let the passive cleave kill them throughout the fight. I was hard burning lich king through phase 1 to be able to get through with as few shamblings as possible. After the shamblings stopped spawning at the first transition, I was going into cleave mode with hammer of the righteous to be able to get them down before the throne room. This ended up being enough damage on them to get them down by the time the second transition had even started; however, this ended up being overkill because they only need to be dead by the time the harvest soul starts.
I'm not sure how accessible this is going to be gear-wise, considering I did this in a full haste setup with 540 item level and the boss still turned into a photo finish burn during berserk. I think it could be done with less for sure but it might take a few more attempts to get a good balance of dps onto the shamblings and keeping good damage on the lich king, since killing the shamblings means you're going to lose a lot of vengeance in the last phase.
Good luck to anyone trying to slay the lich king this week that encounters this problem. Hopefully it gets fixed soon or something because it is a bit annoying to see it change for no reason.