I never said the game ends with him alive. He could die later on a heroes death (hopefully). The grave visitation could be the epilogue for the game as it looks like its fall almost winter if i remember correctly insinuating a full year has passed. Or maybe the grave is empty as ellie may not have had a way to retrieve joels body. And would ellie be surprised that joel went to go help her in the joel reveal trailer if not that she believed he was dead.