I remember there was talk of a side mission involving Asou that was cut, but it's so long ago, I don't remember where the information came from originally.
An interview on the game's website.
It's impossible to tell what it would have been about without asking Shibata (that could be something to do, actually), and it could just be that they hadn't thought forward about it, but the only completed camera ever created just lying around with no further peeps from Asou probably suggests that he didn't make it out, yeah, so it was likely something similar to Ryozo and Takamine's stories leading to their demises. If the plotline was cut so entirely then I think it's likely that any ghost of his was cut along with it, because it wouldn't make sense on its own, really (though if they made it today, I'm sure it would have been stuffed in anyway).
IIRC it says in 5 that he has little/maybe even no sixth sense, plus he's a man to begin with and not a Hinasaki, so it's not like he really could have done much to defend himself even with the most powerful ghost-fighting weapon ever created. Knowing him it was probably Broken Neck coming after him which got him killed. I like the idea of him being taken out by one of the weakest, most garden variety ghosts in the building, and he is a lady killer, after all. I do wish they would remake 1 (however risky that is nowadays) and add it back in, because it would be extra interesting if they addressed Makabe going missing (and not acting like Ryozo has no idea who Asou is), and why Asou still dedicated his life to trying to end it prematurely despite his friend being ritualistically mauled, tossed into literal hell and vanishing without a trace, etc. and if it influenced his research in any way. You're not going to tell me that two of the most eminent occultists (one of whom was directly connected to an old friend of his) never came into contact after 2. Did his 15 wives know where he was going?