Oh, what a good question!! It's hard to say because there's no universe where she would want to fuck him. But, let's say she's drunk enough to have sex with him. If that did happen she would regret it very deeply in the morning and she'd blame Grayson for 'taking advantage of her' even she had consented the previous night. It would result in pretty much the same ending where he runs off to the USA and changes his name.

But, the sex would be incredibly, crushingly disappointing for him. Discovering his mother is just another woman and not the god he'd built her up in his head would probably make him spiral faster. I think this would push him to committing a violent crime against a woman and he'd get caught.