i'd say the only real requirements would be if you can afford to buy a new one, and determining the cause of the old one's death. a lot of stuff is highly contagious, and if you put a new betta in a tank that just recently killed another one, you could end up passing it along to the next guy.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)