Ryu didn't bother to wait to see what the reaction of the young woman would be. He already knew what it would be, and quite frankly, even if he didn't know, he wouldn't have cared to stay regardless.
While he could use his soul to teach that woman a lesson, whether or not he could kill her was quite clear to him. The answer was a firm no.
That woman's soul was easily within the Soul Ascension Realm, swallowing it up with his Soul Birth Realm soul would have been an impossibility. At best, he could cause her a minor injury that would impair her cultivation for a while until she found a method to heal it.
Healing damage to a soul, especially a high level one, wasn't an easy task at all. Unless she had a special Soul Talent, that is. However, in most cases, she would spend quite a while dealing with this. Such was the punishment she faced for her hypocrisy.