The answer of the return of Turin is in your own quotes, Witchking-of-Angmar.
Quote:
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In that day Tulkas shall strive with Morgoth, and on his right hand shall be Fionwë, and on his left Túrin Turambar, son of Húrin, coming from the halls of Mandos; and the black sword of Túrin shall deal unto Morgoth his death and final end; and so shall the children of Húrin and all Men be avenged.
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If he is in the Halls of Mandos, as the quote says, he could be summoned back by the Valar. But it was not the faith of Men to go to the Halls of Mandos. I don't remember what it says when he dies in either the Silmarillion or Narn i Hin Hurin.
If he is in the Halls, he could return.
greetings,
lathspell