Do you think that was the real Kelvin on the island at the end, or just a projection of his thoughts?
and I don't understand why so many people think he was dead at the end. What is the basis for inferring such a thing?
To me, the island is a less-than-perfect projection of Kelvin's memories and wishes by the Solaris ocean. Other than that, I don't know where he ended up, but I doubt it matters. Of this movie, a reviewer once said, "no two persons will see it alike, everyone will take what they need or want from it"... much like Kelvin and the other scientists take of (or are given to by) Solaris itself.