Three Possibilities

In the god temple of the Annihilation God Spirit, the cause-element main god's body was trembling. The other creatures could not see the slash performed, but he knew that if he was hit by it, not only ordinary spirits but also Annihilation-class god temple main gods would be wiped from the history of the universe. They would be cleaned from the history books with no chance of ever recovering.

Even the reviving power of a god temple could not save a life that did not exist.

Demon Alpha's slash was so powerful that it could erase cause powers. If the cause did not exist, how could there be such a result?

Putting aside reincarnation, all traces and prior existences of the creature struck by this hit would be wiped from the records. He would cease to exist, forever and always.

Even the memory of that being in the minds of creatures that knew him would vanish. It would be like that spirit never existed in the sky or on the ground.