We do know that whatever he saw coming in the future, an Azeroth, completely dead and devoid of life was the better option. As much as I hope otherwise, whatever the cause will no doubt be underwhelming.
Oh god, I hope not. That's literally about 2/3rds of the plot of Heart of the Swarm, going to the Zerg Homeworld, meeting the Primal Zerg, learning about the Primal Zerg and becoming Primal Zerg.