[How Imam al-Mahdi (Peace be Upon Him) will deal with the people of the Islamic schools]

The answer: It is expected that his dealing with them will be like the dealing of the Prophet (May Allah bless him and his family and grant them peace) with the people of religions and schools in that era.
So in the first stage of the stages of his dealing with them, he greatly intensifies his calling them to the truth and guiding them to it, and clarifying the proofs and evidences indicating the correctness of what he called to, and the corruption of what they are upon of false schools.
And in the second stage, he spreads the call of truth on the general level in the cities and the villages and the regions, and whoever objects to that, he clarifies for him the proof and evidence for the correctness of his call if he is ignorant, then he forbids him and warns him from objecting and obstructing the call, and all of that is with good speech; so if he does not leave after that the objection in the path of the call, but persists in standing against it, then he threatens and is stern with him in speech; so if that does not benefit, he is disciplined by striking and imprisonment; so if that does not benefit, then by killing and fighting—thus he does with whoever stands against his call, and he fights whoever fights him.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3