It sounds like the owner did everything to save him; at least he had 18 years behind him before he crossed the rainbow bridge.
if Maru crossed the rainbow bridge he’s not in heaven
I can’t imagine how devastated Mugumogu is right now. Maru was her precious baby. Being Japanese, I like to think there is a stern stoicism over the death of a cherished loved one that she is exhibiting. I know I would be a train wreck for at least a few days.
And what will Hana do now? Maru was her everything.