They'll just start taking over the large money-makers (if they havent already): pics, funny, memes, news, gaming etc.

Maybe they'll even create a tiered system of "community curated" subreddits and "official" subs.

Either way, they don't have to moderate the whole site, just the parts that take in most of the traffic. That way you don't have to deal with volunteers and their personal beefs and/or protests to your changes.

Most of the smaller subs are basically dead anyway, in terms of moderation. Many of them are way less active too.