Zhongli's method of saving Azhdaha was brutally straightforward: kill him first, then resurrect him as a Heroic Spirit.
It was the simplest approach. Once done, Azhdaha's Erosion would vanish entirely, and he would fully recover.
"When do we do it?" Jiang Chen didn't overthink it. Since Rex Lapis had decided on this course of action, he would simply help him through with it.
Chapter 163