He has been. End Time, the instance, was a time way that Murozond was hiding in. He stole the Hourglass of Time and prevented us from going into the past. The Hourglass was created by Nozdormu to help defeat him (Murozond) according to his vision. Murozond is dead but since his death took part in the past he can still appear as he hasn't been born yet.
The Infinite doesn't have to die with the death of Murozond as any other Bronze (or Infinite) dragon can take up that helm. It just requires them to find something to grant them powers which is what Dragonflight is exploring. Since the Aspects and those who were never aspects (Black and Green) will be finding a way to get their power back to stop the Primals.
I have a theory that the Titans turn out to be bad and Azeroth is a first one (or something new) that we have to protect. So the Dragons get empowered by the Elements/Azeroth by the end of the expansion. Nothing to confirm it and we will have to see how Blizzard does the story.