"let him go and return to his house": (Let him) heed the words of the Cohein at the battle formation and return.
"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 redeem 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 20:7) "And who is the man who has betrothed a woman": whether he has betrothed a virgin or a widow, even one awaiting levirate marriage, and even if he has heard that his brother died in the war, he returns.