Its a moot point to try to do this because:
1) The attack will render the value of the underlying asset useless, just like a bitcoin 51% attack. The top mining pools have financial incentive to keep going honestly, just as delegates do.
2) If it does happen we can hard fork and start again, ofcourse it would hurt value unless people believe its a bargain and we end up higher because we survived a hard fork attack
3) If they don't do it fast enough they will get fired as they try to collude, if people find out... all it takes is one leak. Its too hard to keep a secret like this when there are so many parties involved.
With points 1/2 and 3 it is less likely we see the scenario play out as CfB wants it to. Is the block signing system more robust than bitcoin's? I think so, does it improve upon the efficiency of consensus protocol? Yes for sure.
If the system withstands itself from this attack (which is probably the #1 on the list of types of attacks on bitshares) then we have a self re-enforcing system that will end up stronger than it was before.
In what case would the system not be able to withstand itself from this attack? The only case I would see is if people end up shying away from the project because it got hacked and wasnt' recovered in a timely manor. Even though their keys would still be intact they may lose confidence... however I find this very unlikely to be the case.