Usually not having the ICP also means your site is dog slow and prone to being blocked at any moment.
Of course if your site is actually needed enough this rule kind of gets ignored. See: GitHub. They probably don't have an ICP license or plans to get one and yet it works really well in China (not even joking)
The original block was way too wide, now they just block gist which is obviously used by dissidents to spread unlawful propaganda. The whole family of pastebin and pastebin-like websites is blocked for the same reason.
Of course if your site is actually needed enough this rule kind of gets ignored. See: GitHub. They probably don't have an ICP license or plans to get one and yet it works really well in China (not even joking)