Everything can be fixed 
The question is, what is easiest? If it's only plasterboard, I would probably replace the board, but if you've done more than just put up plasterboard, repair might be preferable. How big is the hole? There is a special filler that fills deep holes with one application, called "ONE STRIKE FILLER," which I have used. But you must not let filler or anything else get into the socket/box, so it's important to have some form of barrier in between. If it's possible to fill the hole with something else like wood or something to reduce the amount of filler needed, that's good.
The question is, what is easiest? If it's only plasterboard, I would probably replace the board, but if you've done more than just put up plasterboard, repair might be preferable. How big is the hole? There is a special filler that fills deep holes with one application, called "ONE STRIKE FILLER," which I have used. But you must not let filler or anything else get into the socket/box, so it's important to have some form of barrier in between. If it's possible to fill the hole with something else like wood or something to reduce the amount of filler needed, that's good.
One strike filler, or amerikanarn as we call it down here, works perfectly.