User blog comment:Kaido King of the Beasts/Chapter 864: You've Never Had an Enemy Like Me/@comment-5398287-20170502211959/@comment-3986064-20170502223105

I wonder... Doesn't the devil fruit enter into one's blood stream after being ingested and thus allows them to manifest such intriguing powers?

Brook should therefore has nothing but bones so I don't think his DF abilities reside in body anymore. It must be something related to his will at least since he doesn't really have anything else when he's in his soul form. We could also think about Big Mom's lifespan thingy. Maybe the whole thing about Brook is that he gained a power to control his lifespan or at least an extension that lasts more than his flesh body's natural constitution can hold.

Either way, I am inclined to think that he won't die, even if his bones turn to dust.