I think what Nickolai is trying to say is that Jon lost alot of power and alot of range and there is a very small chance that he will regain what he has lost...I think that if you've lost that much range there is no tehnique that you can adapt to hit those high notes again.
But still,I hope that they will return with a new album(i'm not hoping for a KTF NJ etc but something similar to HAND, LH would be great for me) with better production,songs,vocals and do a kickass tour like The Circle.