The way I see it, Guy's body is essentially pure carbon at this point. He was burned to the point of no return essentially. It makes logical sense for the body to naturally die just before his body turned to ash, which is how it was slated to be.
But for Naruto to come by and give Guy chakra without restoring his body.... its damn cruel if you ask me. Now Guy is potentially fully aware of his state and feeling the full effects of the pain, if he's conscious. If he dies he simply has a few moments to live. If he lives he will never be the same again. If Kishi goes ahead and saves Guy, he's likely doing it so Guy can fully pass on his knowledge and techniques to future generations.
But for Naruto to come by and give Guy chakra without restoring his body.... its damn cruel if you ask me. Now Guy is potentially fully aware of his state and feeling the full effects of the pain, if he's conscious. If he dies he simply has a few moments to live. If he lives he will never be the same again. If Kishi goes ahead and saves Guy, he's likely doing it so Guy can fully pass on his knowledge and techniques to future generations.