Who if not Zoro then?
Luffy will deny. Yamato is not the best candidate and she is meant to be out. Momo will likely kill Orochi at best. The Scabbards killing Kaido wouldn't make sense and he would need to be that weakened to let himself be killed by them durability wise.
Zoro is the best candidate unless Oda ruins the arc and Teach does the work.
And Kaido will likely prefer to die by himself rather than being imprisoned. Considering how fiercefully Oda insisted on the death as perfection aspect for Kaido I imagine there will be no weird surprises most likely.