Reminds me of that one time I tried to kill everyone off except the characters who have story importance (i.e. appear more times than in like one or two chapters, then never again) in Awakening to challenge myself to only use those units (that being Chrom, Frederick, Lissa, Robin, Say'ri, Lucina, Flavia, and Basilio).
And the people I've tried to kill just wouldn't die, no matter what I sent them against. XD
Point is, RNG is whack, yo.