If the confrontation happens, there is 100% chance that it does some damage..now, it won't be fatal but at least there will be some damage otherwise there is no point in pitting them each other again if Oda wants to repeat the same scenario as in Udon....and if he can penetrate, there is a high chance that he can penetrate and damage a bit more against Kaido as BigMom durability is comparable or even a bit more than Kaido durability
That's why ever since Oda choose Luffy to learn the GK Ryuou, I can't help but wonder if Oda is secretly planning to make Luffy vs BM instead of Luffy vs Kaido.