I think there is too much importance put on the death of a political leader. Organisations like Hezbollah do not collapse merely because their political leader died. It's not like Nasrallah was some military genius general.
We see this with the Taliban. The USA assassinated their leaders again and again and again. The Taliban only grew stronger. It's not about an individual, it's about an organization and an idea.
Ironically, we also see this with the USA. It's obvious that Biden's totally out-of-it. This has had basically zero impact on America's military strength.
Finally, Hezbollah's all-out retaliation is not happening right now because they're preparing to defend against the coming Israeli invasion of Lebanon. When that happens, they will fight with all that they have. Let's hope they do well. (Edit: Clarified wording.)
Fighting symetrically when you're not symetrical is how Ukraine is losing everything, even then Russia could have killed the entire Ukrainian leadership and NATO will just replace Z with someone else. In the same way, Hezbollah's real leadership isnt in Leabanon, they're in Iran.
Right now Israel is under effectively back breaking economic sanctions, a third of their land is unlivable and they have no path to restoring that. Iran meanwhile is siting back with practically no damage on their own land and joining BRICS while signing economic and military deals with China and Russia.
Iran is doing what NATO wanted to do in Ukraine before people too sensitive to face thought Ukraine should fight a frontal war instead of distributed rebellion. In the long run only victory matters, and victory isnt based on your kill count