I once heard that the Chofetz Chaim has a letter in which he writes that even someone who is totally non-religious, if they are killed because they are a Jew, they have a portion in the world to come as if they were religious. Since they identifed as a Jew (which is why they were killed), they're considered part of the fold.
Where can I find this letter? I skim read Michtavei Chofetz Chaim and didn't see anything remotely connected to this topic. But I definitely could have missed it.
I don't know of a letter, but Reb Elchonon Wasserman is quoted Here as telling his son to make a Bracha before they were killed by the nazis based on the Chofetz Chaim. Also, the Chofetz Chaim's grandson quoted him, as telling those killed because they were Jews in world war 1, to make a bracha before being killed even though it was not voluntary.
Rav Moshe Sternbuch [Teshuvos V'Hanhagos Vol. 5 pg.597] proves from this, that even if one is not given a choice, as long as he is being killed because he is a Jew, it is considered to be "Al Kiddush Hashem". I would say that would most likely get him a portion in the world to come.
