Danny counts on the fact that John doesn't hate him to, I think, actually stop him from doing real harm. Even when he knew his brother was outside, saw the dealer's henchman skulking around outside (prepared to kill him), was angry about that, I really think he expected John to cave.
Or at the very least, keep him guessing about when he'd stop holding his transgressions and cowardice over his head - the same way the entire family has continued to condemn him for Sarah's death.
I don't think he was expecting his little brother to go fuge on him and actually do the deed. He's laughing at John, having fun at the fact that he's got him to snap - and hours earlier John was puking his guts over the knowledge that his brother might've been shot (that he allowed his brother to die) - and then, he casually tells him, "Okay, stop," while he's still laughing.
Like the game is over and they have to reset, go back to being resentful of each other, but generally staying in orbit of the other's presence. It's a comfortable expectation in a dysfunctional family.
But he doesn't, and John leaves him lying flat in the water, doesn't resuscitate him. Has effectively lifted the burden of Danny's existence from his shoulders, and he can't quite believe it himself.
And it's like, rather sad, because how does this show keep moving without this Dante/Vergil-esque feud to fuel it? Bloodlines is a rather middling, but exciting (to some degree) show, but a lot of it was kept alive by the Danny/John dynamic. The reveal that Sarah's death was accidental just happens with little fanfare - mainly because the family appears to not care to look at it any other way as 'Danny's fault'.
The father dies, and barely lurks as a narrative consequence afterward. The mother is so weepily passive that the subplot about her leaving the father doesn't figure all that much into the story beyond why Danny took Sarah out on the boat. How did she evade so much blame?
If Danny's not there to haunt the narrative in life, what does his death lend the show once he's gone?
