C2801 Surprise
With Huangfu Yan's personality, he would very likely make this choice. If he didn't fight with Bai Yu Zhe and only wanted to escape, then it would be very difficult for Bai Yu Zhe to kill him.
The other option was to just guard outside the formation and wait for Huangfu Yan to come out. Since he was cultivating inside, it was impossible for him to not come out for the rest of the day