Tamgotchi - where art thou?

"It will definitely be dead by now" Jennifer announced matter-of-factly as we discussed the whereabouts of the Tamagotchi she has nurtured to 4th generation - but had not seen since the weekend - when it goes back to daughter Sophie for her care. When I saw Jennifer on Wednesday she realised she had been without Tama all week, and then it was Thursday and the acknowledgement that even virtual creatures need TLC if they are to survive. But how much? How long can you keep a Tamagotchi going? Have the programmers worked out the average lifespan - of the carer's commitment? Is there a secret prize if you successfully nurture the Tamagotchi and its progeny to a certain point? And what's the best/longest life for a Tamagotchi? And where can I buy one (or perhaps Jennifer and Sophie will loan me theirs. When they find it.)?