This Onmyoji was severely injured, but not to the extent of damaging his core.
Just as Ling Qingyue said, practitioners of their level generally only experience a slight effect on combat capability as long as the core isn't injured. Even if their hands were cut off, their destructive power might still be formidable.
However, once the core is damaged, it becomes quite troublesome; it's not easy for masters to get hurt, but once injured, recovery is very difficult.
The Onmyoji's core wasn't damaged, but he didn't know if Ling Qingyue's core was harmed. Ling Qingyue's strength left him fearful, causing severe injuries during a sneak attack, yet she managed to send back his Shikigami with a single strike—truly impressive.
So, when the Onmyoji and that upper-level Ninja discovered others were tunneling in this cavern, he didn't dare rush over, fearing Ling Qingyue wasn't badly injured.
