I don't think the Gura Gura will respawn. I remember reading that there DF energy in the DF, can't quite remember if that was in the manga, if Oda said so, or if it's a theory, but I remember seeing the term. So, assuming that it's true, my personal theory is that Blackbeard pulled in the DF energy from W-Beardo's body, and stored within himself. This is possible cuz Yami Yami allows him to pull in objects, store them in the darkness, and has a direct effect on DF powers even when it's consumed. It also struck me as weird as to why Oda would make BB a Logia, but he doesn't have the benefit of intangibility. Like, why didn't he just make it a Paramecia? That's when it hit me, since the DF energy, and by extension, the DF power, would be stored in the Darkness created by Yami Yami, Blackbeard needed to be more than just capable of making and controlling Darkness(Paramecia), he needed to also BE the Darkness, hence why Oda bothered to make him Logia.