Famous authors can write for the international translation market, essentially. A few months ago there was a submission about Yan Lianke's struggles: https://news.ycombinator.com/item?id=18206445

It's still possible to read banned books on the mainland if you know the right sites, but most consumers of banned literature are probably just looking for porn, so you might need to do some digging to find something more high-brow.

I'm not sure what lesser-known authors do, but I guess they try to keep their fiction as fictional as possible.