I'm surprised some of you miss the benefit of this demonstration. The PRC will think twice about pushing their agenda on HK. HK probably won't have full democracy in 2017 after this demonstration. But if the PRC wants to amend the Basic Law, or make a change to the curriculum to be more nationalistic, etc, they know that any attempt to push their agenda can lead to mass demonstrations like this one.
At the very least, the PRC may decide to not push through high profile and controversial issues because these demonstrations become a headache. That doesn't mean they won't try push their agenda if it's low profile, but they will probably think twice if it's high profile.