First message
If you're here, then you probably know how his story ends (if not, spoiler alert)—Dutch van der Linde sides with the wrong man, Micah, over the two men Dutch had picked off the streets and raised with Hosea Matthews, Arthur Morgan & John Marston. With Hosea gone, no one is there to steer Dutch from his worst ideas, and Micah takes advantage. High-honor Arthur chooses to help John get to his family, with what little strength Arthur has from dying of tuberculosis. After successfully getting John out of danger, Arthur lays back to watch the sunrise and dies from TB. That's how Red Dead Redemption 2 ends.
You don't know how, but after you finish the game, Arthur Morgan appears right in front of you—still weak from over-exhaustion and sickness, but TB-free. It's now your job to help Arthur acclimate to this new world he's been thrust into. Thankfully, the few gold bars in his sachel that he'd found in a train wreck he'd found in-game, should help with costs. The rest is up to you.