@Triceron:
Oda's never played ball that way. In almost every other situation where characters are assumed dead or killed in action, Oda has never hinted in those scenes that there is any possibility for survival. Survival happens afterwards.
No, he USUALLY plays ball that way.
Almost always right before it happens, or in the very next chapter. Again, I point to Luffy declaring "You don't know that Bon is dead!", the tongue pirate being up in the next chapter, not actually showing the Going Merry crashing against rocks, Blackbeard having recruited Shiryu BEFORE getting poisoned and lots of dialogue about having cures for Magellan's poisons, Ivanokov revealing he/she can deflect poison thats already hit by removing some heavy makeup, the only witness to Sabo's death being REALLY far off and no body and a prior setup with Dragon being in the area and having met Sabo… even the gag danger like Sanji's near death from nosebleed was setup with chopper giving him multiple transfusions beforehand, in single gag panels here and there for a couple chapters before it became "serious".
Even if its a line of dialogue rather than a visual, or just a single innocuous panel, Oda generally plays fair, often in subtle ways. (The most subtle thing he's ever done IMO is there being three sake cup shadows when he was only showing two.) Hell, we got notification that Arlong was officially alive years later from Hachi mentioning it offhand. (Or that Arlong has a sister is a single one line offhand mention that had no bearing on anything else, but its there. Its a little minor thing that says a lot to those paying attention.)
Similarly, he gave us a very definitive vivre card and said "that represents life force" so that he could be absolutely 100% clear that Ace had just died, despite logia intagibility. (In case the giant fist through the chest wasn't enough.)
Plus, Ace died with a speech and a smile saying he was content, and those are requisite. And with Whitebeard, he gave a huge speech, and when he died, Oda gave us actual narrator text boxes, he didn't leave that one to characters just talking.
Or, when one of the main crew vanishes for 10 chapters, and they come back at the last minute having done something important, (Like Sanji turning the water flows at Enies Lobby, or Franky waiting outside to catch the lat minute bit) it works because... Oda had them leave for an appropriate ammount of time and set it up fairly.
Even Pell who is the go to whipping boy on this, was shown to be alive a mere 8 chapters later... but even that was only a single panel showing his head scarf, not Pell himself. Which could be, and IS, overlooked by anyone not paying attention. (And to this day people are still confused about finding out he's alive much later in the story, because they miss that half page and overlook that single panel... or 30 seconds of anime.)
It's the same with the deadly gas. We are not given any hints that the gas isn't effective or that it hasn't killed the people it's already affected. It's common knowledge that Kinemon won't die, but there's no visible cues or hints that Oda has left to lead us to believe that; we simply believe it based on past experience.
We've been given at least two.
Luffy was partially hit by the gas and only partially and temporarily effected, and he's fine. (And Franky's mech, but that's a mech.) That's the subtle visual hint. And Ceaser had a line of dialogue about it not being deadly till a secondary effect kicked in oh, 20 chapters ago before it became the ongoing threat for a long period that you're supposed to have forgotten about since he said that months ago. Those are the subtle ones.
The huge easy authorial "I've studied Oda and know how he operates" hint is that it hit a main hero character. And if he can be saved (and he can) then everyone else can as well.