To be fair, no one survived from the Old Kingdom. Everyone had to meet their end at some point. Terem was born and raised in Wasteland at the end of the kingdom (they're a little younger than Stewie) so they were kind of doomed from the start.
I suppose you don't know the story that's in my head though. The big picture story of my AU is this:
Tempest born in modern times
As I mentioned here, I headcanon winglights are the souls of past people who died but got trapped on earth. One of the wnglights that Tempest picks up is Terem's soul.
When they're a couple months old, Tempest gets curious about the past and starts trying to figure out what happened, how/why the kingdom fell, what life was like back then etc.
At one point while flying in Wasteland, Tempest gets hit by a falling shard which causes Terem's memory to unlock and Tempest relives Terem's whole life in a dream.
When Terem dies, Tempest wakes up again back in present times (they had been rescued from the shard by some older sky kids).
The rest of the story is about Tempest processing what happened (dealing with grief and healing), trying to ascend Seed and Lookout to Orbit, try and find Terem's spirit (lost in the world and almost faded away) and ascend it too so the family can all be together (Tempest does succeed at this), and trying to fulfill their destiny of helping to restore/heal the Sky Kingdom (the destiny of all modern sky kids).
So the whole story is about grief, healing, destiny, family, and remembering and honoring the ancestors and about how no matter how small and short, every life is worth living and the story of every person is worth telling.
So even though Terem dies, it's not the end of the story--Terem lives on as a story/memory and as a winglight soul within Tempest (and later as a spirit that can be interacted with and ascended just like any other spirit).
I want to write this as a comic, but unfortunately I am in university so my time is limited and my art skill is not up to snuff yet, so for now I just have to tell it as an outline, random art and worldbuilding, and comic drafts.