Interesting twist. Normally, a story like this would end with the heroes finding the ONE ironic weakness that the seemingly indestructible villain possesses, and using it to overthrow him. In this case, they don't bother finding his one weakness - they just maroon him on an island. So he's STILL indestructible as far as they know, but it doesn't matter, 'cause he's cut off from them by hundreds of miles of ocean.