I'm creating a datapack on this very concept, one that can detect the void and apply Levitation X, which successfully saves me from the Void without taking damage. After you can press shift which would allow you to disable the Levitation and safely land back onto an End Island. Mind you this was applied for a specialized Netherite boot, which detects an NBT on the player's feet. You can change it to detect a specialized totem and have the same effect applied. You will have to find a way to trigger the totem after use to not make it op. You may also yoink it from me if I ever do get the chance to post it.

It might be possible to have players manually place a command block that executes levitation effect when player is below ~ -80 ~? If its possible for convenience you could possibly have the datapack place the command block at 0 0 0, and a force load command at 0 0?