But every so often, our mitochondria and their
  surrounding cells fight. The result is diseases,
  such as mitochondrial myopathies (a range of muscle
  diseases) or Leigh’s disease (which affects the
  central nervous system).

It's not clear to me that mitochondria are fighting their host cells in a myopathy. They simply aren't working because of genetic mutation. Even if we do say they are "fighting", it's not obvious why that is a result of them originating from two different cells.