The owners of Bitcoin exchanges are not performing chimpanzees at a tea party. If a fork occurred and two chains were similar size then the CEOs of Bitcoin businesses would quickly agree (with Core dev and the mining pools) which chain to use (B) and which chain to ignore (C) , even if this meant suspending trading in the meantime.

This is why Gavin has consulted with many Bitcoin companies/players already, to find out what their view is. He reports that they support scalability by a big margin. Bitcoin businesses are going to want their business model to have the best chance of success, and that does not include crippling the tx throughput on the blockchain which wil also cripple business models.

The rejected chain C will quickly find that the difficulty (40+ billion) is way too high for the devoted "anti" rump of miners clinging to it, and it will take several hours to mine each block. This will get worse as the coinbase rewards can't be sold for decent fiat at any significant exchange. Miners will to drift to the majority chain. It will probably take 1 year for the difficulty to fall on chain C until it is usable. So chain C will need to be forked in order to slash the difficulty for the few users who still want the 1MB lmit.