Don't confuse cex.io with ghash.io. These are two separate issues.
cex.io is part of ghash.io
The ghashes people trade on cex.io are hashing for ghash.io
I'll try to make it clearer. The OP and the point of this and other threads is the hash power not the potential for someone to gain or lose trading at cex.io. It is completely irrelevant if everyone sold their cex.io hashing power today at a loss or gain. Ghash.io would still have the hash power and possibly even more incentive to do something untoward with the blockchain. People are pointing their own miners to ghash.io. That's what OP wanted to figure out how to stop, or at least slow.
cex.io is part of the problem, I was trying to convince people to stay away from the place and keep their money out of it. This is not going to stop the miners they already have but would probably slow down their expansion.
About 3 weeks ago a sell off at cex.io started which saw the price dropped from 0.072 to 0.032 at the end of last year. 2 days ago I noticed ghash.io had 33% network share and today 40%. Coincidence?