This makes me, yet again, want the idea that it's not rape if he reasonably believed he had consent to be changed. It means that the only one who really has any power, is the rapist. Why is his belief held in higher esteem than the woman's?
In this case, she didn't even know. I think, that without positive evidence of consent, that it's rape. If you're drunk, and you're thinking about putting your penis in someone who's drunk, you should make sure you're damn sure she consents, and err on the side of caution.
I think thats entirely realistic, because I have been very drunk, and never inserted any part of myself in someone else who wasn't happy for it to be there, both at the time, and the morning after.
I have been very drunk, and had parts of other people inserted in me, which I was very happy about, both at the time, and generally the morning after (albeit sometimes with a bit of a face-palm).
If I punch someone in the face, even if we're both drunk, it's assault, unless I can prove, and they agree that it was a mutually enthusiastic fight, and even if it started mutually enthusiastically, if it turns out that they was too drunk, or that I hurt them, I can still, quite rightly be prosecuted. The law about assaulting someone with a penis should be the same.