A plague has killed most of the Earth's population, leaving one man, who fears he may be the last person alive.
Does that plot sound familiar? No, its not from 'I Am legend'. It is from a much better book called 'Earth Abides'. It does not have any vampires, and there is no Will Smith.
Many years ago I read this classic science fiction novel by George Stewart. It is very well written and made a great impression on me at the time.
The story is that the main character, Isherwood Williams, returns from a trip in the California mountains to find that a plague has killed almost everyone. There are no undead, just dead. Williams eventually finds other survivors, sets up a colony, and tries to rebuild civilisation. He succeeds in some respects, and fails in others. The book ends with Williams as a dying old man who realises that men come and go, but Earth abides.
The book was reprinted in 2006 and is available from Amazon.
For a scientific view of what would happen if we all disappeared you should read this article from the New SCientist.