What do you think the consequences should be for the Marine? Obviously it would depend on the reason for the accident. If it was a technical weapon malfunction, the Marine is not to blame. This happened to an F16 pilot during the Kosovo conflict. His HARM missile malfunctioned and landed in a house in Bulgaria. Fortunately no one was injured in that one either.
What backlash will be produced from this event? If the Marine was not culpable, since no one was harmed, I doubt there will be much backlash. From the article, this happened
at the range itself. So, only government property on the actual bombing range was damaged. I'm kind of surprised this even made international news.
Edited to add: I read another article on this incident and apparently the bomb actually
hit the ground, not a building, though some damage was done. So, in a nutshell, a marine dropped a bomb on a bombing range in a remote location in Australia. The bomb hit near a military control building on the range, and the title of this article is 'U.S. Fighter Jet Bombs Australia Building'. Interesting. I'm surprised that didn't add 'as the US president applauds the performance of the Marines'.

Journalist tricks never cease to amaze me.