We do have 4 witnesses back in the top 20. In theory that is enough to stop a future hardfork. In reality, all Justin Sun needs is have a few million steem or SP distributed in enough accounts and in a blink of an eye and a click of the mouse and he's in the top 20 again.
We need at least 17 witnesses in the top 20 so a new SF can be installed to prevent future abuse by Justin Sun. But many people seem to be happy with just 4.