This thought has been on my mind for a while though but for the world's whose keyholes were already sealed (Traverse Town, Deep Jungle, Wonderland,etc) and the worlds that were destroyed but brought back didn't need to have their keyholes sealed so my question is with how powerful Xehanort can he unlock all of the keyholes again or because Sora sealed them/they became hidden securely are they completely  sealed

it opened once, it can happen again

It could be done again, but no-one really has the need to destroy worlds' hearts. They might bring it back but since the KH created through that method is a fake their wouldn't be much point apart from general chaos.

Honestly, I never understood which Kingdom Hearts was the *real* one, anyway. Granted, I've only played BBS once, but it seems like that's the definitive version, but I've never heard of the Kingdom Hearts at the end of KHI being a 'fake'. I'd attribute that to Xemnas' artificial Kingdom Hearts, which was basically hand-crafted by Roxas, Sora, Xion, and himself.

Edited November 3, 201311 yr by Kaweebo

This thought has been on my mind for a while though but for the world's whose keyholes were already sealed (Traverse Town, Deep Jungle, Wonderland,etc) and the worlds that were destroyed but brought back didn't need to have their keyholes sealed so my question is with how powerful Xehanort can he unlock all of the keyholes again or because Sora sealed them/they became hidden securely are they completely  sealed

NOOOOOOOOO, THATS TOTALLY NOT THE REASON THAT THE DESTINY ISLANDS GOT DESTROYED BY DARKNESS AFTER BEING PEACEFUL FOR THE 14 YEARS SORA AND CO. LIVED ON IT.

 

Of course its possible, thats what Riku did and thats how the islands got destroyed by darkness in KH1.

NOOOOOOOOO, THATS TOTALLY NOT THE REASON THAT THE DESTINY ISLANDS GOT DESTROYED BY DARKNESS AFTER BEING PEACEFUL FOR THE 14 YEARS SORA AND CO. LIVED ON IT. Of course its possible, thats what Riku did and thats how the islands got destroyed by darkness in KH1.

But the keyhole wasn't sealed and it made it easier for it to be destroyed by Riku

If they can be unlocked before logically you can unlock them again, that's how keyholes work.

While I see it being used as a plot to revisit old worlds again (seal the keyhole again), like at the end of KH3 some catastrophic event unsealed every world leaving them vulnerable to attack and thus we have to go to them again