You have the right idea by mirroring the left side of the picture, but you don't need to mirror all the detail - doing so makes a picture look unnatural. I'd stick the mirrored duplicate into its own layer, and then delete all detail that is OK in the right hand side of the image, leaving only the detail lost by the tear.
bedlam123 is right about there being no quick fixes. Complex editing such as this is fiddly and takes lots of time. Thankfully, however, it is not difficult... unless you are short of time, of course...
