I say this because most of the characters have flaws or issues...and it seems that when they get these flaws/issues worked out...they "die."
Last night, Locke made a reference to the fact Richard was no longer chained up...and he seemed to indicate he was either the devil or a high ranking demon.
Throw in the word "Dharma"...and all the foreshadowing that includes...and somehow...I think this is some Buddist/Christian hybrid purgatory. I really do not think the answer can be "scientific." I think it has to be "spiritual." A scientific answer would be rather anti-climatic.
...Except the creators of the series have already come out and said that is not the case.
I think that was a popular theory but season 4 shot it down, don’t you think? Once people from the Real World showed up, alive, how could that theory work?