Here it's not freedom of speech in China that is at stake; it's freedom of speech outside of China that is at stake. But Github will no doubt find it hard to foot the additional bill indefinitely, and there is a noticeable degradation in the liveness of their services. What should they do?
You can imagine them braving a DDoS attack like this for a few days. But governments have trillions of dollars at their disposal, and the match in this case is probably an uneven one.
Should governments concerned with protecting freedom of speech step in to help out with the costs of a company like Github maintaining business as usual in the face of such attacks?
(I am not affiliated with Github in any way.)
[0] https://status.github.com/messages