How madara escaped hashirama
Eternal MS doesnt give unlimited izanagi. That would just be retarded.
You wouldnt be able to die in battle, unless of old age.
We know madara gave both eyes to nagato, so he hasnt used izanagi to escape Hashirama (that would have cost him 1 eye).
I think he used muu his splitting jutsu for an escape.
We know he has fought vs muu in the past, so its possible that he copied it.
Madara has a grave in konoha (which makes me assume they buried his body there).
The grave is at the picture where uchiha Setsuna and some other rebels are standing.
Google translate turns the word MADARA into マダラ.
Which is what is written on the grave. The symbols on the grave are the name MADARA.
Kabuto got hold of the dna of madara.
How does he get hold of that? How can he do that, when madara was still alive, a few years passed kakashi gaiden and died in his cave, unknown to konoha?
Nobody would know where Madara was, nobody would be able to get his dna.
If madara used splitting jutsu, than there would be a body to bury and that body could be used to steal dna from.
Meanwhile the other madara(split) has been alive for a while in the cave, plugged to the gedo mazo/flower.
Madara used muu his splitting jutsu to escape hashirama.