On the day that flight 815 crashed, Kelvin was planning on ditching the island on Desmonds' repaired sailboat, the Elizabeth. On this day when Desmond followed Kelvin to the cove, he accidentally killed him. Desmond then ran back to enter the numbers just a little too late causing 815 to crash. I find it safe to assume the cove as a valid location on the island--we see the Losties crossing it a few times, later the Others, Kelvin docked the sailboat there and let's not forget that a hostile Miles was also discovered there. The distance between the cove and the Swan is probably almost an hours journey on foot. I base this on the fact that Desmond had to run back to enter the numbers, and he was still late. Because of this distance, I find it unlikely that Desmond would venture out to bury Kelvins' body due to the time constraints. It is only after the computer is nearly destroyed that Desmond finally returns to the cove to board the Elizabeth and flee the island and the Swan (or so he would like to think). Which brings me to Kelvin.

Where did his body go?

Did Desmond actually have time to return and bury Kelvin?

Or did he just slough his body into the ocean?

I find it odd that our characters visited the cove on a few occasions and have not seen a dead Kelvins' body. Perhaps his body was tapped by someone or something and removed the corpse from the location in the same way Yemi and Christian were moved. Hopefully, you know what I'm getting at by now.

Where is Kelvin?