Yes Israel should have taken out Nasrallah at their "victory" celebration in Beirut. Nasrallah is a coward for not coming out of hiding at such an important time. He never goes anywhere near the front lines. He prefers to let Hezbollah's young men do all his dirty work for him. If Nasrallah dies, I wonder if his death would throw Hezbollah into dissaray. Maybe they don't have an adequate successor to fill the void.
Nasrallahs death is very bad for israel and the west. Believe it or not, nasrallah is seen as a moderate in hezbollah. I dont think it would be great to replace him with more hardliners, which would surely be the case if he is assassinated. Hezbollah has to be destroyed with him at the helm and no one else should be able to take his place.