If they're treated like any other publisher, probably having that many workers manually vetting everything won't be viable. Which is fine, because it shouldn't be. It confuses me how every time we have one of those posts about how horrible that work is for the people doing it, most posters kinda throw up their hands and go "well whatcha gonna do" when the obvious answer is... simply not do it? If your business requires that, the easy answer to how to not cause that harm is to not have the business.
If the survival of their company depended on it, they would absolutely figure out a way to pre-moderate content, and almost certainly that would include significantly more low-paid moderators.
They had something like $18 billion dollars in profit last year, you don't think they could afford to hire an army of moderators?
I reckon they can afford 150,000-200,000 more moderators, moderator-managers, workers on and managers of tools for same, et c. before that profit margin starts getting mighty thin. Is that enough? I don't know, maybe it is. How long before profit hit zero would investing in Facebook start to be considered a poor use of capital, since that's the actual tipping point? Also not sure.