Although he blew up the Nexus energy, it didn't destroy the world, injure Willow, or cause any harm to the world whatsoever. What it actually did was erupt like a volcano, and Zion controlled the eruption to kill every angel in the middle world.
His senses scanned the entire planet, and he confirmed that all the angels were dead, or had managed to flee to the upper world in time to escape his wrath. He didn't care about those who fled, though. Sooner or later, the entire world would be his, and he'll deal with everyone who doesn't follow his way soon enough.
Using his divine power, Zion healed the land, restoring its former beauty. Though the destruction was still there, the world didn't look like hell anymore.
"I have to meet up with Lilith." Zion went into his fracture and then traveled to the demon world.
When he arrived, thankfully, the place was unharmed and was only recovering from the death of three Archdemons.
