That's not to say you can't have some recovery and adapt, just that what you were before is never coming back.
I developed diastolic dysfunction and severe sensitivities and food intolerances after Cipro and other antibiotics in 2014. The only way there could be a persistent diastolic dysfunction is if there has been permanent damage to the cells of the heart.
If he has input as to things which helped him I'd love to see, but as far as I understand, if the mechanism is indeed mtdna depletion and mutagenesis from excessive ROS then I don't really see how you actually cure that.