It's that "Do your duty" comment that makes me truly believe Brienne changed her mind at the last moment.
Just because we saw Brienne swing the sword doesn't mean she actually killed Stannis. And because they didn't show us, it's almost certain that he did survive...
There is every possibility she swung the sword either out of frustration, or to intimidate Stannis, but had already decided against killing him right there and then, so she fell short of her mark intentionally.
Of course, they might be deliberately doing the cliché moment only to turn around and tell us she really did kill him. Anything is possible.
I guess I put myself waaay out on a limb by pronouncing Stannis dead. Brienne's cry as she was swinging Oathkeeper could very well, as you observed, have been one of frustration. As much as she wanted to avenge Renly, her knightly sense of honor may have kicked in and prevented her from completing the act.
Then, Stannis had not been relieved of his weapons, only the ability and strength (and apparently the will) to use them. Those sentenced to death are rarely armed when the execution is carried out. Stannis' confession to the murder of Renly should have cleared Brienne's conscience for what she was about to do.
To quote Dan Weiss himself: “In a show, everybody sees it for what it is. It’s that rule: ‘If [you] don’t see the body then they’re not really dead.’
I appreciate how the showrunners like to mess with our minds in their off-camera dead-or-not scenes. I don't know if they are religiously following their "no body, no death" rule because I have no doubt that Shireen is gone, not that much of a body would have remained to display.
I must be subconsciously following the rule, though, because I was unsure it either Tywin or the Hound was dead at the end of season 4. They produced Tywin's corpse in the season 5 opener, but I still hold hope for the reappearance of the Hound.
Maybe it boils down to how everyone feels about the character in question. I hate Stannis for burning his daughter alive, so I want him dead. I like the Hound, despite his checkered past and motives in protecting Arya, so I want him alive. Everybody loves Jon, so, regardless of the convincing pool of blood in the closing scene of this season's finale, fans (myself included) universally want him resurrected ASAP and by any means possible in season 6.
Working his return into the opening credits would be nice.
Thanks for the links. Both the video and the article were insightful. I liked the sense of humor displayed by the producers and cast members in the panel.