What does Vardaman fear will happen now his mother is dead?

Vardaman is traumatized by his mother's death and copes in his own way. He associates her death with the fish he caught that day, and sees the reality he "knows" in the fish was alive one moment, dead the next, then cleaned and unbloodied with his mother. Everyone is confused by his constant chatter, but to equate something he knows with something he doesn't understand at least succeeds in making it bearable. Vardaman eventually makes it even more bearable by envisioning his mother is a fish. A child's imagination.

Jewel’s mother is a horse,” Darl said.

“Then mine can be a fish, can’t it, Darl?” I said.

“Then what is your ma, Darl?” I said.

“I haven’t got ere one,” Darl said. “Because if I had one, it is was. And if it was, it cant be is. Can it?”