They are expected to live 2-4 years. Some have lasted over 10. The animals don't usually breed, but some have. Supposedly they can't continue indefinitely because certain molecules gradually collect in certain forms and don't get 'unlocked' like weather events do for them on the Earth. I got mine from a place called Greenfeet.com which was a little cheaper than the creator's website linked above.
That site also has an article by Carl Sagan written after he bought one.