well at the time it was mentioned he had a illness that affected his throat somehow so he couldn't carry on but looking now it seems to say that he was suffering with depression and a few other things and he just decided to leave randomly

Here is a very interesting link with some info on who will be the new singer for Killswitch Engage, and it`s from an official source so it`s not made up.
https://www.roadrunnerrecords.co.uk/page..._id=117586
i can`t say i saw that coming i figured they would have got someone new entirely, not unwelcome news though.