I think King Harald didn't Die,
We've seen this Harald vs Loki in every Single Kingdom before,
Wapol vs Dalton
Cobra vs Koza
Gan Fall vs Wyper
Neptune vs Hody
Doffy vs Kyros
Orochi vs Oden
And in each of these Kingdoms there was a "Hidden Area" that Outsider Villain was interested in,
(In Drum Island Case, We don't know what Blackbeard Found there)
Tomb of Kings in Arabasta
City of Gold in Skypiea
Treasure Room in Fish-Man Island
Smile Factory in Dressrosa
Underwater Area in Wano
So WG want Elbaph also cuz of some kind of Treasure there, (It's almost always some Place Below just like Examples i mentioned above),
But what's interesting is that Rebel Guy never ever Succeeded in taking down the King, their Encounter always ends Unresolved or not in Rebel's Favor, it's unlikely it happened now, especially when it's revealed that Giants aren't allowed there & there is only Single Survivor
I feel like King Harald became a Pirate & He can only be Man With Burn Scar, which explains why No One knows him,
And i still believe He is Lurking Legend that Oda spoke of, cuz He is only Hidden Top Tier who could have met WB only among Top Tiers we've seen so far
If it was Loki or Imu or Xebec or Garling or Shamrock ... etc Oda wouldn't single out WB to describe this Villain's Past,
Harald is Only Candidate so far, and i can feel that slowly in each Arc He is Hyping him beyond Top Tiers
Actually i might go a step further & say that He might be Final Villain,
I know that 99% of Fandom will disagree, but let's wait & see till We find out more about him
Don't forget that One Piece is inspired from Vicki The Viking Cartoon,
King Harald is clearly inspired by Pirate Villain of that Cartoon called "Sven The Terrible" (He resembles him more than Blackbeard does)