Alma 24:26

And it came to pass that the people of God were joined that day by more than the number which had been slain; and those which had been slain, were righteous people; therefore we have no reason to doubt but what they are saved.

That day God’s people were joined by more people than had been killed. Those who had been killed were good people. So we have no reason to think they aren’t saved.

That day, more people joined God’s cause than had been killed. And those who died were righteous, so we have every reason to believe they’re saved.