I'm not sure what he can say though.
To play devil's advocate, if I were his PR I'd have advised him at the start to get out in front of the allegations, not contest what was in the public domain and issue a grovelling apology for any harm he had caused. The fandom might have bought that if he had done it early. There is more joy in heaven over one sinner who repenteth...
I wouldn't have advised him to fight back unless there was some factual claim that he could disprove.
Going into hiding and hoping the thing goes away might be his only option, but it's really not a good option. It invites more allegations, maybe to the point where his creative partners can't sustain silence any more.
One thing about Johnny Depp was that he had a long list of ex-girlfriends who went on the record to say that Amber Heard's account wasn't the Johnny they knew. That didn't by itself disprove anything Amber said - it's likely the two of them were a uniquely toxic combination. But it did mean there wasn't similar fact evidence to bolster Amber's case, and much more rested on her own reliability as a witness.
You notice that's not the case with NG. He has a huge number of celebrity friends, and none of them are popping up to be character witnesses for him. Some more minor creators who could do with his patronage are wondering why they didn't spot the signs, and the really famous ones are staying absolutely silent. Maybe because Neil has asked them to.
I wonder at what point we'll start to see TV shows being quietly cancelled.