Immediately following death, the soul enters the eternity of heaven or hell and what happens to the body does not change anything about that. Furthermore, many Christians have had their bodies burned in death, either through tragedy or martyrdom. Nevertheless, I would always encourage people to be buried simply because the biblical pattern should be what we adhere to.
In contrast with the pagan cultures around them who burned their dead, burial was the practice of saints throughout the Old Testament and the New. Burial expresses the preciousness of the body. Christ has redeemed our body, so it has value. Furthermore, burial expresses the resurrection of the body. One day it will rise again to be reunited with our everlasting souls.
Where possible, let us follow the biblical pattern.