All that would accomplish is taking control of the revenue generated while they are in control. If the big mining centre is working with private keys that are u

All that would accomplish is taking control of the revenue generated while they are in control. If the big mining centre is working with private keys that are unknown to the operators, then they would not be able to spend the coins previously mined. If they gain control of more than 51% of the hash rate in this way, they would be able to censor transactions or reorg the chain. That would still leave most of the blockchain in tact. A deep reorg might even get forked away from by the rest of the network, leaving them alone in a situation analogous to Ethereum Classic.