So both Doc Brown and Marty contemplated killing Mad Dog Tannon but they both seemed to forget that he's the great grandfather of Biff Tannon. So by killing him they're also killing Biff. Good thing Marty just knocked him out instead of killing him, huh?
"I'll be back!" The Terminator
I don't recall either of them planning to kill Buford.
shareContemplating it and planning it are two different things. You can contemplate something for a few seconds, before deciding against it.
I guess the OP is referring to the fact that at one point Doc has a gun pulled on Buford. And also that Marty agreed to a gun-fight with Buford.
Marty is easy to explain. When accepting Buford's challenge, he had no intention of going through with it. He arranged it for a time after he was meant to have gone home. So when it transpired he did have to fight him, Marty came up with another plan. One that didn't involve killing him.
Doc, though he was threatening him with a gun, probably didn't intend to kill Buford. As long as Buford believed he would, the threat stood.
I was more thinking of maybe if they had Biff wouldn't exist. Though I guess it's possible Maddog Tannon might have already produced Biff's Great Grandfather.
shareNo, I understand that if one of them had killed him, Biff wouldn't have been born.
But neither of them did kill him, and like I said possibly neither of them really intended to.
Either way, as Mad Dog was not killed, the future stayed the same.