"lest he die in the war": If he does not heed the words of the Cohein, in the end he will die in the war.
"and another man will inhabit it": I might think, his son or the son of his brother — It is written here "another," and elsewhere (Ibid. 28:30) "another." Just as "another" there is a gentile, so, "another" here.
(Devarim 20:6) "And who is the man that has planted a vineyard": This tells me only of one who has planted a vineyard. Whence do I derive (the same for) one who inherited, acquired, or received a vineyards as a gift? From "Who is the man" (— any manner of man).