The end of Tokyo Ghoul "manga"

What happened to Kaneki at the end of Tokyo Ghoul's second season?

It seems that a lot of people want to simply write this off as speculation, with no proof that Haise Sasaki is indeed Ken Kaneki's new identity in the sequel who survived the conclusive battle with Arima and is now serving as a mentor at CCG under Akira Mado 2 years later.

Below are some brief hints from chapter 8 volume 1 (which has Sasaki on the cover) of Tokyo Ghoul:re without revealing too much. I find these to be a bit more than mere 'speculation'.

Haise Sasaki begins to notice past self:

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Note the mention of a 2 year time span and an amnesia like state questioning about a past life of friends and family, as well as paternalistic Arima:

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