Everything. Gone.
Just like that.

Skyverworld is a datapack that changes the overworld to be a series of islands of varying sizes and heights over the void. It also changes the loot tables of ocean ruins to include kelp, since the ocean biomes are completely dry and thus don't generate it. It's also completely beatable in survival, unless the island it spawns you on leaves you no opportunity to get to another one.

Also, if you're using this for a YouTube video or a heavy reference for your own datapack or whatever I ask that you please credit me because I worked really hard on this and if you don't, I will cry. Do you want that on your conscience?

And, if you want more floating islands in your life and Minecraft worlds, check out skyther, a datapack that does this but for the Nether.