The ratzon of Hashem isn’t that he die. The ratzon of Hashem is that a yehudi should kill him. Not a non-Amaleki gentile; and not himself.
Which is another reason he shouldn’t. Because if he does, he is denying the mitzvah to a yehudi. What I would encourage though, is that he should turn himself in to any yehudi and allow him to do it and obtain the mitzvah.