I feel like he would let John kill him so he could be with his family. John wouldn’t want to but Arthur probably would say things like I’m not worth it or no one will miss me and let himself be killed.

That’s why I think they should redo Undead Nightmare with extra quests to do with people who died in RDR2

Well, he’s not. He’s buried in Grizzlies East, Ambarino, in a remote place. Nowhere near Great Plains or Tall Trees. I personally do NOT want another Undead Nightmare. They’ve done that now, and I didn’t enjoy the original anyway.

Based on the good honor ending of Red Dead 2, I doubt John would kill Arthur. He'd probably just bring them Arthur's hat or something and say he's dead and Arthur would leave the midwest.