You're not getting my point lol.apparently they found a way
It's a canon manga fact that nobody knows how to destroy them. So they can't.
The Poneglyph is whole, so it's either on one half or the other... or it fell into the ocean if it was located right where the island was cut in half.
In fact, now that I said it, I think that's how it'll be. Since it wasn't listed as a reward, we can reveal in WCI that Onigashima had a poneglyph the whole time... and that if it's not there anymore, it must have fallen into the sea.
And then we can make it a reward later on and center a story around it.


