Even without absolutely no help from healers, if you pop/have active a single buff(bulwark, sentinel, foresight, rampart) or SS yourself before DS hits, you will not die with full HP.
WILL NOT.

And no, DS, plummet and AA will never activate within .5 seconds lol. Not even close. DS's cast alone takes longer than .5 seconds. Nice try dude. Ask questions, cool. Don't insinuate

something else is wrong apart from your lack of experience tanking twin.