the client's 'invalidateblock' debugging command - possible prevention against majority attack? there is a 'invalidateblock' debugging command in the btc client. How can this command be used in a situation of majority attack threat and play a part of countering the attack? 

I understand that this command lets nodes 'ignore' blocks generated by the attacking miners. But is that it? What happens with the blockchain, how can it continue to live on without the majority attackers?
If there’s a case of a majority hashrate, human intervention of a single instance can not prevent something that continuous and ongoing. The amount of coordination required to keep the network in consensus would be impossible to obtain if this were a solution. 

If Bitcoin fails, it’s time to move on rather than patching it up.