There is a logical reason why the god of fate should be killed apart from the unforgivable hatred between them. Killing the god of fate will grant Legion total control of the Zargoth plane. So it is highly beneficial to see the current Celestial dead.
Aeternus's determination to kill the god of fate sealed his fate. Even that single future disappeared after Aeternus spoke. The future vision of the god of fate showed nothing but darkness after Aeternus made up his mind to do the deed. The god of fate has gone from having numerous futures to having none at all.
The god of fate laid down flat on the ground and sighed. "Just get it over with." He murmured.
Aeternus was perplexed. He asked. "Aren't you going to run or defend yourself? Stand up and fight."
"It's no use. I'm doomed."