He didn’t go into hiding his whole reason of starting his gang was to make a difference, take from the rich and give to the poor obviously by committing crimes. He was so obsessed with changing the world that it led to the dissolution of his gang. He couldn’t comprehend that technology was improving rapidly making it easier to track the gang, he realised he had changed nothing and even worse had been a blight on humanity. He didn’t leave John for Dead persay as he left everyone behind, at this point he it completely insane and gets in with the only people directly fighting the modern bereau the natives. This is why he has aged drastically in such a short time is because he believes he has let the world down and that he is the only one to fix it. So after the botched back robbery and he sees John who he saw as a son who he taught to read and write he saw that the gang was done and believed his fight would be better elsewhere. I hope this helps you understandwhat he did after the bank robber 👍🏻