Clearly it's not an issue for individual humans to know. There are already mixed factions with humans in them. Obviously some humans already know. Presumably it's only a problem if
The Masquerade is broken. The guy telling his tavern buddies that "demons are real! I met one!" isn't any different from some guy in real life insisting that he was abducted by aliens. Related, I notice that we have human factions like the Church of the Day devoted to exterminating non-humans. So it's already more than individuals. There are entire organizations out there that know, but the "consensus reality" is that such things aren't real and the common man doesn't believe it. I suspect it will take a lot more to break the Masquerade than yet one more raving drunkard saying that the churches are right, demons are real.
I wonder though, about factions like the Seekers. If they're here to promote racial harmony, presumably breaking the Masquerade is part of their goal. Not sure how you can have harmony without the majority of humans even knowing the rest of us exist.
Ahh, here we go:
Some humans know. Like sorcerers.
So yes, some humans know, and some humans are not only aware of magic, but able to use it too. If Avery takes Victor into the fold, it's business as usual. If he doesn't, it's still not a big deal.