Blackbeard reaches Raftel before Luffy to find that the One Piece is not what he wanted it to be. He gets furious that his dream is crushed and remembers Whitebeard’s words “You’re not the one Roger is waiting for”.
He then storms into Marineford alone and uses the Gura Gura no mi with its FULL power to complete Whitebeard’s fight and wreck Marineford down to dust. He gets killed by the 3 Admirals combined in the process. 3 skulls, 3 fruits, 3 powers, against the 3 admirals.
I don’t think Luffy will defeat Blackbeard like other villains, it doesn’t mean they won’t fight. Since their first meeting, I had a good vibe from Blackbeard and his dreams speech. I only see him dying in the place he killed his father in. Redeeming himself for killing Whitebeard and Ace.
It may sound farfetched, but from the recent Shanks scenes, the final pirate enemy could be him, not Blackbeard. It doesn’t mean he’ll be a villain but he could have a different view from Luffy resulting in a major conflict between them. Luffy and Roger want to turn the world upside down, unlike Shanks. This could be the reason the World Government leaders are willing to meet Shanks as he shares their view.
It would actually be poetic if all the remaining D. Clan members died (Law in Wano as speculated – Blackbeard in Marineford) except the last 3 Monkeys (Garp – Dragon – Luffy) which will destroy the Celestial Dragons and the World Government to set people free.
*Theory by boburr1233