Well after running heroic Blackrook hold (heroic daily) and Mythic Darkheart Thicket I'm not as worried. I actually set a few record kills. This may be because of better experience with the fights or good RNG. I also continued to run Prot as my "healer" and didn't have that much issue. I can definitely feel the healing and damage nerf but I think fights should still be able to be completed.
I recently unlocked my 2nd golden relic slot on my dks and I chose Umbilicus Eternus. It gives me an absorb shield for 5x the damage that my blood plague did during the duration of vampiric blood. I wasn't thinking it would be that powerful on a boss/one target but it is stupidly powerful. I get about a 1.8 million absorb shield for 10 seconds on a 50 second to 1 minute cd. I haven't pulled a lot of mobs to see how high I can stack it. I'll have to do some testing with it and double dancing rune weapon since I can use that and get 3 sets of blood plagues on my target. It does take a bit of timing and does not instantly absorb the damage but with 45-50% extra healing and hp it would be hard for something to one shot me during vamp blood. I expect it will greatly help my toons catch up on healing and to buy me some time where i cannot melee or aoe heal my toons and to ignore a mechanic every 1 minute or so during a fight combined with AMZ it can be quite a lot of ignoring and extra damage time.
I got a several Mythic +2 keystones that I'm going to be trying out this week. I got 2x Blackrook Hold 2x Neltharion's Lair and 1x Maw of Souls. A few guildies got some 860ish gear from completing the keystone.