Fulgora at a minimum is 50% of hakai. And look at the circumstances. Look how much damage zoro took while blocking...Meanwhile Kidd took 100% without blocking and continued fighting.
And regardless Zoro never tanked hakai.
1st of all where did you get the idea that Kid took Fulgora head on? What we know that both Kid and Killer were caught in it but none of them took full damage they were just blown away.
And how did you come to the conclusion that Fulgora is 50% of Hakai. If you say its the scale then you are wrong. Fulgora's scale looked bigger than Hakai. Which i don't think it translate to damage. Hakai is a direct attack aimed at them. While Fulgora is an AOE huge attack that was aimed at Onigashima where Kid "should" be.
And to the answer the topic. If Zoro didn't block hakai no one would die but they will be injured and law eventually swaps them all damaged. Zoro just bought them time in his expense.