Curious as to how much will it hurt when the dental anaesthetic wears off, after root canal treatment?

That depends: I have had patients who dont have ay pain after a root canal. And then I have had some with severe pain after a root canal. It depends on how much instrumentation is done beyond the apex of the tooth, how inflamed the nerve is when the treatment was performed (the longer one waits to get a root canal, the more likely it is to hurt after), and your pain tolerance. There are medications to help.