Even if Gongsun Mo manages to escape unscathed this time, it's likely that the forces behind him will find a bone to pick.
It wouldn't even be necessary for Li Fei to act; the power behind the scenes would eradicate the threat by themselves. If they still wished to remain hidden, they would surely do so, and it's quite possible that Li Fei might appear unexpectedly to catch the other party off guard. At that moment, Li Fei also wanted to see how his adversaries would respond to him.
The reason Li Fei chose to handle things in this way was simply because Qi Nian Hall's initial plans were too naive.