While you make a valid point if you apply real-life physics, it poses a problem, if dehydration was an issue for the victim, wouldn't the case also apply to the culprits as well? Remeber, while the extraction ritual was underway, the Akatsuki members could'nt physically move, and they had to remain concentrated on the ritual. They couldn't eat, drink and had to remain mentally focused during this as well... If anything THEY were more at risk of death from lack of nourishment than the jinchuuriki.
They didn't need to be perfectly concentrated, Remember Itachi and Kisame used used some sort of clone jutsu to fight Team Kakashi and Team Guy Respectfully.
Also only two of them were actually physically there, Sasori who has a puppet body and thus no longer needs water to function and Deidera who for all we know may be drinking out of one of his mouths, plus we know that all of them are not needed as when they were extracting Gyuki form "B" there were only three of them, it is entirely possible that they take small brakes to drink rehydrate.
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With Kushina however, you got other things to consider; the seal was already weakend by the labour of childbirth, and Obito is an Uchiha augmented with Senju cells, and knowledge of jinchuuriki seals which he obviously gained from Madara. He struck at the opportune moment and with Kurama free enough to place genjutsu on it, Obito didn't have to exert that much effort to break the seal. What the manga has so far confirmed is that it is the extraction ITSELF which is fatal to a jinchuuriki, not the MANNER or DURATION of it. If the later two were the case, than I would wonder why Obito was ultimately so surprised to find that Kushina was still alive.
True the weakened seal could affect the duration but it could also be the reason Kushina survived as long as she did. After all while Obito would have had to have been told how to extract a Tailed Beast by Madara, from what we know Madara never extracted a Tailed Beast from anyone much less extracted one from a Jinchuriki who had just given birth.
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Which brings me to my previous post; while I don't believe Kurama's chakra is that much different from its brethren, the fact is that it is the strongest of the Nine, with almost limitless chakra, and as such is perhaps the only Bijuu that must be sealed within an individual descended from the Sage's lineage. Think about it, all of Kurama's hosts have been Uzumaki clans(wo)men, and before them Hashirama Senju controlled it, and Madara Uchiha before him. Now that I think about it, have you ever wondered why Kurama is the only Bijuu so far that can be physically summoned by contract? Perhaps further evidence of my above theory.
True but there is one wild card, actually two, the Gold and Silver brothers, somehow they were able to retain Kurama's Chakra from eating parts of his stomach, someone else from Kumo tried eating one of Gyuki's tentacles and died, either the Gold and Silver brothers are also descended of the Sage (which is possible) or there is some other factor in the mix.
As for the summoning, we are told that all the the Tailed Beasts are capable of using the Tailed Beast Ball/Bomb but we are not shown if Skukaku can, does that mean he can't? no it just means we haven't seen it and on that same merit we know that Kurama can be summoned with the Summoning Jutsu be dose that mean that the others can't no, it could just be that Madara was the first one to summon a Tailed Beast using the Summoning Jutsu. Of course that is just speculation, we would need more evidence to know for sure.
It's not speculation the uzumakis do survive after they have the bijuu extracted this is not speculation this is a fact stated by obito himself.
There are just to many wild cards for me, like I said to Quinny52 the fact that her seal was weakened at the time could be a reason she did not die automatically, furthermore we would have to see ether Naruto or B have there Tailed Beast extrated via the same jutsu in order to determine if
- A Jinchuriki is supposed to die immediately after the extraction or if they can survive a while after the extraction
- The state of Kushina's seal had anything to do with how fast the extraction was.
- Furthermore if you recall Kushina was special even among the Uzumaki clan, how can we determine if her surviving was something that runs in the entire Uzumaki clan or if it was like Hashirama's Wood Release where none of his descendents received even though it was a Kekkei Genkai
Another factor is the translation, as we can see with recent chapter between MangaPanda and MangaStream we have to very different translations, yes Obito was surprised that Kushina was able to survive, but I've read a translation somewhere where he also attributed her survival to the Uzumaki clan's vitality. But it was never stated in any translation that she would be able to survive past the night, Even she didn't think she would survive the night.