I have not observed this firsthand, but have read that in the serious 'end' stages of heat stroke, many animals do not pant or pant only very weakly. :(
For your roo, the buff orpington-- a purple comb usually indicates a heart problem, as the heart cannot keep up with the body's need for blood. Did he show any other symptoms? Weakness or paralysis of his legs? How old was he when he died?
It is hard to know what happened with Clarence. Heat...