Or it would still be technically removing the evil that has affected his family as they wouldn't be around at the end of the next thousand years. Or maybe there's another reason that the seals on the stone are breaking and Graham could seal it forever. Whatever the case, I do think that Graham will be sacrificing himself to end the evil that has oppressed his family. It just seems to make the most sense with the foreshadowing and Graham's emotions and dialogue.
Just editing in a thought that occurred to me (because double posting is of the devil) that might explain why the seals on the stone aren't holding and why Graham may need to sacrifice himself. There are the twelve signs of the Zodiac (and in the game, the dark stranger mentioned the twelve Silver Cloaks that sacrificed their souls to the stone) but the truth is that due to the elliptical path of the sun through the constellations, there is actually a thirteenth Zodiac sign. Kind of like a leap year sign. So if the writers are going the route of the Zodiac and that kind of astrological mysticism, it could be that one more sacrifice is needed to be the thirteenth sign. Heck, maybe the dark stranger was a Silver Cloak and was meant to sacrifice himself along with his comrades, but wimped out at the last minute, which is why the evil was only held for a thousand years and now the bonds are weakening. He failed and is disgraced and now Graham has to take his place and keep the evil contained forever.
