I feel like Takumi left it here on purpose, as to maybe get feedback on the ending, so...
The way Reimu drops the marble leads me to believe that the consequences of her actions hadn't sunk in. Like an undisciplined child that isn't -really- bad, just untrained and unrefined. But, Takumi, so without further adieu:
BAD END: Anon abyuses koReimu until death, koMarisa dies, anon is sad, rain washes away the scene.
GOOD END: Anon abyuses koReimu until death, koMarisa wakes up, says something to anon. Anon smiles, perhaps buries her, maybe considers adopting another stray.
INTERMEDIATE END: Anon abyuses koReimu unil death, koMarisa is still alive and is healed by anon. Anon takes koMarisa home with her bauble, both live happily ever after.
PACIFIST END: Anon is about to abyuse koReimu, until koMarisa calls to him. He decides it's more important to save his friend than to abyuse koReimu in revenge, leaves, takes bauble, keeps koMarisa.
PACIFIST END II: Anon is about to abyuse koReimu, until koMarisa calls to him. koMarisa says something to him, he smiles. KoReimu comes over, apologizes, cries, tries to give bauble back to koMarisa, but too late, koMarisa dies. Anon (maybe?) keeps koReimu (or the bauble, possibly both).
TRUE PACIFIST END: Anon is about to abyuse koReimu, until koMarisa calls to him. He decides it's more important to save his friend than to abyuse koReimu, who in a moment of clarity after a near-brush with death, realizes what her greed did to both of them, and apologizes. Even gives koMarisa's treasure back to koMarisa. Anon, seeing that perhaps she's capable of learning from mistakes, takes both home. Both become pets, though Reimu still has a little bit of (cute) bratty in her, but all three become close -- Bronze Reimu and Silver Marisa.
But it's likely going to end with everyone dead except anon.
Oh, yukkuri and their ridiculously self-destructive scum logic... Makes for effective story conflicts, but barely makes any sense otherwise, lol.
It would be ten times easier for mother Reimu to simply steal the marble and puff at komarisa to scare her away rather than going out of her way to kill and shit on komarisa.... It's hard for me to understand how this is a sensible trait to develop even for scum, and it kinda clashes with the idea that a yukkuri is supposed to be a social creature that likes taking it easy.
Stuff like this makes me headcanon that scum yukkuri actually have a literal mental illness, rather than their malice actually being a sane, learned behavior. It's a wonder the aggressive ones don't die out from being too stupid and impulsive to avoid unneeded conflict and self destruction.
I kind of hope Reimu's mate is only gone because she just left her for being aggressive and unlikable.
It's a Takumi thing more than yukkuri comics in generals. Not that 99.99999% of yukkuri comics don't end with horrible death for all yus involved, but most at least try to aim the abyuse at shitheads, even though any nearby niceheads inevitably end up dying too. Takumi on the other hand loves to lean into the sadistic side of things, he specifically goes after yukkuri that are innocent and kind.