A fan of John Byrne, Cory Vandernet, made quite a discovery recently in his studio closet - a handwritten list by John Byrne of some future storylines planned for X-Men all through issue #150 in 1981.
As you all know, Byrne's last issue on the title ended up being #143, so those plans never came to fruition.
While the list had some intriguing ideas (including some stuff Byrne has spoken about in the past, namely getting the available original X-Men back on the team (Iceman and Angel) and some stuff I had never heard of, like the multi-part "Robot Cyclops" story), Byrne went into depth on one particular story idea, and the idea is available on his board's FAQ here.
Byrne relates a story that involves Sabretooth (who, at the time, had only appeared in Iron Fist) attacking Mariko and brutalizing her (just violence, no sexual assault or anything like that) to the point where she's pretty much dead.
The X-Men find her, though, and get her hospitalization, but she's in a coma - brain dead. And Xavier cannot do anything to help her, and when Wolverine doesn't believe him, he connects Wolverine to her mind, so he can experience the emptiness.
Wolverine, naturally, cuts her life support, then goes off and, in a bloody battle, kills Sabretooth - with the reveal then coming that Sabretooth was Wolverine's father.
It's pretty similar to Chris Claremonth's take on Wolverine and Sabretooth, that the two were
Father and son. That's why Sabretooth (*my* incarnation, that is, not this "Creed" poseur) always considered Logan "sloppy seconds" to his "original" / "real deal." The other critical element in my presentation of their relationship was that, in their whole life, Logan has never defeated Sabretooth in a knock-down, drag-out, kill-or-be-killed berserker fight. By the same token, on every one of his birthdays, Sabretooth has always managed to find him, no matter where Logan was or what he was doing, and come wihin an inch of killing him. For no other reason than to remind him that he could.
Therefore, this is the one time that Wolverine finally beats Sabreooth - spurred on by the death of Mariko.
And all of this was to occur in 1981.