What is Zed? An assassin. What other assassins do we have in the game? LeBroken, Kha'Zix, Rengar, Talon, Yasuo. What was the difference between those and Zed? They could assassinate you later in the game if played properly because you couldn't deny 1 of their key abilities. What did Zed do? Ult you, do damage, get out and then you popped Qss and lifesteal back to full HP. Also, Zed is extremely telegraphed with his ult. Now Zed has the same chance of killing you as other assassins. So, deal with him as you would have dealt with Rengar, Kha'Zix, LeBroken or Yasuo. Simple as that.
Also, all those i mentioned are assassins... ADCs are not supposed to survive their all-in on their own anyway, assassins are designed to kill you fast if you overstep. So, mind your positioning and never wander around alone.