OK, I see where this is going. However, I don't think this would be as easy.
Now everyone in the network switches back to the bottom chain, and the miner switches to mining the top chain. The miner can keep doing this until the fork becomes ridiculously long and the data between the two chains is completely incompatible.
Once the community notice this happening, they will most probably ban the faulty miner (blacklisting their IP or something similar).