Well, the legend is that one where the guy goes down into Hell to save
his beloved, but she'd already eaten down there, so he couldn't bring
her back. :p  Don't remember their names, because I don't find Greek
history all that exciting - Greek and Rome just copied each other's
legends. ;p

But there's another point you forgot - Ranma wasn't in Japan when he
met that Death woman, and so the time would be off, totally. (Unless
she specifies Japanese time, but they weren't in Japan, ne?)

And ... well ... I don't see how it fits with Ranma, that legend like
that. Using Japanese gods, legends, etc would all work much better...
I don't know, maybe Susano could take that Death goddess' place? But
I think that the family would have at least got a shinto priest or
ten around to ward off demons (which is really what this 'goddess' is),
and throw beans at her and stuff. It's Japan, and they're Japanese
after all ... it's really hard to mix non-Japanese mythology with
Japanese characters because they're so different, and they Japanese
customs mean dealing with things in totally different ways. *shrug*

Kun-chan...