I don't know if the snake is dead. But Sasuke after Itachi's death told his team that "we have left snake behind." What ever that means.
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Ah that's Madra's statement. We don't know if he is telling 100% truth.
...summonning capacity= Uchiha seem to have power over nine tail. While first Hokage could tame all of them like his pets. That's why Madara fled.
I only wanted to touch on afew of the points you brought up.
1. I think that was more of a reference to them, as a team, leaving Oorchimaru behind and moving forward together. I coul be wrong. I wish I had Sauske v Deidara fight on me.
2. Very true, Madara said it, but O could swear Itachi validated it. Think back to when Sauske first heard of Magekenyo Sharingan, it was Itachi who told him about, and I could swear he included Madara's story.
3. I really wouldn't call what The First and Madara can do to the Bijuu an ability to "summon" them per-se, but more an ability to control them. Arguably, if I had to chose one I'd go for control myself, but that's not the point. In order to be able to summon a creature, as far as we know, one must have a contract with it.
Which brings me to an interesting thought: What if Naruto gains the ability to summon the Kyuubi?
Think about it, were not quite sure what will happen once the seal is removed/unlocked on Naruto. Killerbee and the Eight Tails have a very symbiotic and amiable relationship, so what if you could actually summon AND controll a Bijuu.
This makes sense in this way: Akatsuki wants to use the Bijuu to control the shinobi wars. However, they are sealing all of the Bijuu in a statue. So... what good does a Bijuu in a statue do? Not a lick. To cure this problem you devise a summoning Jutsu. Okay, now the Bijuu I want is out. Lets say I summoned Sikaku (because I like Garaa). I command Shikaku to do smething and he smiles poliely and flips me off. Now I need a way to control him.
Arguably the Bijuu are stronger in their raw forms than encased in a human being.
Arguably, as well, this could not be what Akatsuki is planning at all. Perhaps they only need the Bijuu as a "battery" of sorts to power some weapon or empower some Jutsu. I mea, could you Imagine what Shinra Tenei could do with the chakra of nine Bijuu behind it? Eeek...