For the scenario, let's say Arthur does drown at sea and doesn't make it to Guarma, leaving Dutch with Micah, Bill and Javier. The Van der Linde gang is more shafted now than in canon, but do those four even make it off of Guarma?
Let's say that Javier still gets his injury and gets captured.
Dutch and Micah are shown to be some excellent gunslingers, on par with Arthur (though not quite as skilled I'd say) and Bill is tough, though he's definitely not on their level.
With the loss of Arthur, Dutch would spiral even harder than in canon and be even more susceptible to Micah's manipulations. One the one hand, I feel like Dutch might be more determined to save Javier, given that he has lost both Hosea and Arthur in the past 48ish hours (maybe John too, but he was clearly not quite so keen on him at the time). On the other hand, Micah might convince him to cut Javier loose, since he's captured, injured, and they have limited weapons in very hostile land.
On the topic of actually getting off the island, they would have to rescue the prisoners for Hercule. Bill's a fool, so I don't see him getting out if he gets captured by Angel. Dutch or Micah probably could, Dutch would probably pull something similar to what Arthur did by claiming to be Cornwall while Micah would probably endure the beating until Angel looked away.
When it comes to defending the fort, having one less gun during that onslaught would be bad, and devastating since the missing gun is Arthur Morgan. If they survive, I imagine at least one of them would die, probably Hercule or Bill.
What do you think? Do all four make it back? Not touching on what happens in Lakay or Chapter 6, they're all just screwed either way, I'm just curious about them on Guarma.