I've always disliked the idea of punishing groups for the deeds of individuals. Doesn't make sense to me.
Apart from that, even a banned Pakistan could get into controversy
.
As far as ICC handling goes: a ban and possibly a fine. But the British criminal court is not about cricket or cricket results. Butt, Asif and Amir have been found guilty of conspiracy to accept corrupt payments and conspiracy to cheat. The criminal trial was merely about making money by rigging bets. People who rig bets should be considered as major criminals. I can't say I find the jail sentences harsh.
The only thing I can think of as a proper defense, is for Amir. He might very well have been under a LOT of pressure by Butt to conspire with him.