But remember the Traveler could have taken her power away anytime but it didn't. Maybe there was merit to her plan for the survival of the traveler. Sure its selfish of them but remember she's also smart. She has her own plans but she doesn't go out to just destroy others. Whatever plans she had its leaned more (probably through the Light's influence) into the doom of the Witness. She thinks its a losing battle against the Witness anyway and she even warns us of it. If this is like the last Traveler and we're wrong and everyone loses the Light, is that worth saving us for that brief moment? . The Traveler was also smart in its own way how Sathona didn't know she was worthy before. Savathun didn't take Light from it, it gave it to her. It had plans for her. If anything I don't think the Traveler is some helpless entity to be overpowered by Savathun. And so if it does just use her for survival at our demise, maybe atleast it could still bring Light to others in the future. . At that situation atleast its not a total lose. But since we're already here its probably gonna be some deus ex machina Vex thing.