Frances
"I have devised a solution... More of a simple band aid to our problem of an amputated arm but one nonetheless." 

Irapx would say and hold out his hand, creating a hologram of a keyhole out of light magic. 

"As some of you may know... There is a keyhole in every world. *Where* Said keyhole is in the world is transient... It doesn't stay in the same location. Once Heartless get to this keyhole then the world is doomed to fall into the Realm of Darkness... All living things on that world turn to Heartless."

Then with dark magic, he'd made a black sphere enter the keyhole and dispelled it altogether. 

"There is a chance for those with powerful hearts to not die... But to end up in another world called Traverse Town; which is also under threat of falling to darkness now. If we can seal the keyholes then Heartless won't be as attracted to that place... Leading to us being able to cull the Heartless present and take back that world; making it a safe zone like how it appears to be Deep Jungle is currently. This also means that powerful Heartless are likely lurking in those zones in wait to find the keyhole or feast on the hearts of those knowledgeable to seek it out. Locking/Unlocking a world can only be done with a Keyblade, so if those special Keyblade users did defect then somebody could come up behind us and undo our work."
William
*Yumi, having come back, had decided to just sit and listen in. She didn't have a keyblade, none of them did, but she was able to help fight back at least.*
Crystal
The nobody glances over at all of the people here. Do they have keyblades, too? It is difficult to gauge the rarity of such a thing.

"I would suggest that you gather keyblade wielders, if you lack the tools to do so yourself."

The more keyblade wielders, the more hearts that are set free.