I think he’s dead. But the legend was the entire crew vs the world and then losing thru betrayal. The island God Valley prolly dissapeared bc he had the Yami Yami No Mi. And that’s why teach got it (inherited will + historical knowledge)
If that was true, Whitebeard vs Blackbeard would have hinted at Whitebeard knowing about that Devil Fruit or recognizing it belongs to his previous captain... And if you think Oda didn't prepare for that back in the day, you're wrong cause WB had a flashback in Marineford where it HINTED that he was WORKING under someone and he was not a captain by the fact someone was calling him "Newgate" and not "pops"
Xebec has his own powers, not the Yami Yami no mi... Otherwise, Oda would have made WB recognize that fruit or comment on it...
Also, Oda would NOT bring such a big threat only for him to be in the past only LMAO, that's not how shonen works, they always end up showing up...
Lastly, my idea in fitting BB into Xebec is that they both will form an ALLIANCE, while Shanks and Luffy will form an alliance, then we will have:
- SH + Red Hair vs BB + Xebec
Luffy + his idol vs BB + his idol
And I firmly believe that in that battle, both Luffy/BB will surpass both of their idol as them both being the last two standing