>>55448846THEORY:
Sada went to the past, Turo went to the future. Even if one is dead, the AI takes their place in going there. Unscratchable metal is from the future, sent to the past and buried. They did this because even though they separated over conflicting aspirations, they both knew they met because of researching Heath's book, which wouldn't happen without that tablet. Even though one will die, they want to ensure they will meet so that Arven continues to exist.