In my opinion ALL 5 KAGES WILL SURVIVE,
but kishi is using "outer-extras" to save the kages lives.
REASON? To make MADARA LOOK BADASS AND POWERFUL AS WE HAVE ALREADY SEEN
Extra helps for Kages:
*Release of Edo: Helped to stop the perfect Susanoo Rampage
*Oonoki's Super Jinton (with tsunade's help): that wiped out 25 level 2 susanoo's..... IN MY OPINION THE KAGES WOULD MOST LIKELY SHOULD HAVE DIED HERE.
*Byakugou: Tsunade has never shown this till now.
*Dan: Dan saved Tsunade, after she saved the other 4 kages..... Anything else has to be said?
this are some stuff that the kages have been pulling out of nowhere, or have been lucky of getting it with perfect timing.
HONESTLY, I think Kishi's intention is not to kill the 5 kages, but to make Madara look STRONG AND FORMIDABLE. The same way he did with Pain during Pain's Arc..... For example: Pain fought an entire village and destroyed it. Later he fought Naruto with 2 Sage Mode Recharges+Intel, still beated him. Until Naruto transformed into 6 tails, pain was barely handling it, but in the end still came on top. Later the 6 tails transformed into 8 tails and then fought another sage mode naruto. IN THAT MOMENT NAGATO, still had enough chakra to fight Naruto (proof: Gedo Rinne Tensei on whole village).......
THIS IS A PROOF OF HOW POWERFUL NAGATO WAS AND HOW HE DIED, WITH NO ONE IN THE VILLAGE DYING...........
SO I THINK KISHI WILL DO SOMETHING LIKE THIS WITH MADARA, MAKE HIM LOOK ALMIGHTLY STRONG, PUT ALL THE CARDS IN THE KAGES SIDE TO MAKE THEM WIN.