I believe he attempted to save Islam but that Islam was not saved at the end, well not at least was his intended goal, he intended to steer the nation back on course and rose with hope that was crushed and to risk in accepting the promises which ended in betrayal.
Imam Hussain, however, showed we should be willing to take risks and ready to sacrifice and lose everything in this risk, in shaping the destiny of humans.
It shows the path of courage which is the path Quran calls to.
In this sense, all Imams and their example and legacy was an important part of keeping the true light alive. The light although not very much people truly see it as it meant to be seen, is still alive in some hearts, and can be found if you search the truth in Quran through the help of Sunnah. In this sense the religion remains strong in the sense clear proofs and way to knowledge of it remain while in the past, the truth would become so hard to find, and there would be no easy means as opposed to today.
As for the apathy - of doing nothing and just watching oppression - as opposed to rising for justice and striving in God's way, as for apathy and just watching and not forbidding evil and command to good- according to Quran and Ahlulbayt (as) they share and are put under the same crime as the oppressor.
Islam and apathy don't go together, neither is the mockery of God's proof or belittling God's verses to the extent of misplacing them all from their essential roles and place in the Quran.
Courage in times of when shadows rule and try to scare humanity - we are going to need a lot of it if we are to change the destiny of humanity into easy victory where most benefit, instead of destruction of most with saving of a few which has been the track of previous warnings.