<p>Brilliant question.</p><p>
</p><p>i think he was starting to go mad before the game (possibly when he killed Heidi McCourt for example) although it was fairly minor, and the gang still functioned well. However, I think that the impact of hosea’s death should not be underestimated - he was the one holding Dutch together all those years, and his death stopped Dutch having any rational influence and released the nihilistic part of his personality. Although it was always there, it was no longer suppressed after Hosea wasn’t there to suppress it (Arthur and John both say that Dutch becomes more who he really is, supporting it). Additionally, Hosea’s death opened the door for Micah to exploit and get in dutch’s head, destroying the gang from the inside.</p><p>
</p><p>i think that the effect Micah had on the gang in terms of being an informant for the Pinkertons wasn’t as big as many people think - he had contributed to bringing down the gang from the inside, and the information he gave to the Pinkertons seemed to have less of an impact than the internal divisions had, as this ultimately led to a standoff within the gang.</p><p>
</p><p>overall, Pinkerton pressure and their murder of hosea, growing insanity from Dutch and Micah’s corruption of Dutch all contributed to the gang’s downfall, but I think Hosea’s is ultimately what did it - the gang was on its last legs by beaver hollow and didn’t need a rat thanks to internal divisions, the latter of which was mainly caused by Dutch and Micah, and because Hosea wasn’t there to prevent this from happening </p>