What are all the ways in which a gold block can be removed in vanilla Minecraft?
I was way overthinking this. Catching all block breaking events is not necessary. One only needs to store the locations of each placed gold block and then check every hour if that location still contains a gold block.
I'm assuming that commands are not allowed.
Can players reach the End?
The Ender Dragon has the ability to break blocks. These are just removed and disappear.