I was looking back at the fight now that the official translation is out.
Didn't Who's Who scream after being hit by demon brick fist? Or is the "gyaaa!" from someone else? Oda used the same sound effect when Kaido was getting hit by the supernova in the rooftop fight so I'm pretty sure that was Who's Who screaming, which confirms he wasn't KO'd.
Also, we didn't get a single panel of Who's Who reacting to demon brick fist. Usually when a character is KO'd, we see their face. But Oda didn't do that for Who's Who even though he easily could have with the final panel. Rather, the final panel was of jinbe.
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So overall, I'm really willing to bet that he will either use awakening or the innate regenerative power of ancient zoans to heal himself and continue fighting.