Has there ever been proof that the fourth is dead? As far as I know there are no pictures of his fight with the Kyuubi, the sealing, his death or his dead body. When Orochimaru and the third fought Oro summoned three coffins out of which zombiehokages emerged, the one hokage not shown is the fourth. Why is Kishimoto refusing to show us direct evidence of this persons death? Minato is to Naruto what Jesus is to Christianity.
Well if he is alive the first question probably is: why did he fake his death?
A possible explanation is that he realized there was a conspiracy behind the attacks and he chose to fake his death and leave the village in order to pursuit the conspirators who were probably not expecting him this way. Another explanation is that he was one of the bad guys himself and staged the attack to seal the ninetails into his son. Even if he sealed the Kyuubi into Naruto for virtuos motives we still dont know them, so dont come and say "why should he?"
However I can't really imagine that Minato was evil so I personally prefer the first explanation.
Bottom line, I find it extremly suspicious that we haven't seen hard evidence for the fourths death.
If this theory already has been discussed please forgive me.