The key thing to remember is that even with perfectly timed heals (that sweet spot where the tank has taken damage but the infirmary debuff isn't applied yet) the tank can still die. I've seen Twin combo DS + another attack for just shy of 7900 damage on an i89 paladin before, so the number I keep in mind is that the tank needs another 900 or so health to survive DS 100%.

So you need to have the mitigation ready beforehand. If you have a warrior debuffing Twin you're already most of the way there. Or better yet, a warrior MT who is also debuffing Twin, as the warrior can intercept every DS with a cooldown, while paladins cannot. The worst scenario is double paladin, but good use of adlo and stoneskin can bridge the gap. Just be mindful that Twin will sometimes delay a bit and knock all your bubbles off before using DS.. you may need to reapply it.

Once the tank has survived DS and brought above, say, 50% health, you can mostly relax. Bellyflop won't kill a tank at moderate health and there's time to patch the tank up once infirmary drops.