Which is preferable: following the imam in adding to the prayer, or opposing him?

This happened to us once in prayer—O Shaykh—Next: The imam prayed with us—may Allah reward him with good—and at the beginning of the second rak'ah, he realized that he was not in a state of ritual purity, so he withdrew and brought in the mu'adhdhin.And he said to him: He restarted the prayer, so he said the takbir and repeated the prayer from the beginning. All the praying ma'mums prayed five rak'ahs because they were confused about what to do! Except for three who prayed the four-rak'ah prayer and opposed the second imam; they completed four rak'ahs and did not add the fifth with him.Meaning: They sat down after completing four rak'ahs and did not continue with the second imam. After that, one of the brothers who had some knowledge stepped forward.So he said to the brothers who prayed five rak'ahs: You must all repeat your prayer.So one of the brothers said to him: They were confused, and all they had to do was follow the second imam to be safe. So, is it considered that they intentionally prayed the fifth rak'ah, and therefore they must repeat the prayer? Or was their following of the second imam a matter of caution, and therefore they only owe the prostration for forgetfulness? What is the best course of action?
The best course in this situation, if the imam remembers that he is not in a state of ritual purity, is to appoint someone to lead the congregation for the remainder of the prayer without restarting it. For example, he should say to the mu'adhdhin or to someone behind him who is able to lead the congregation: "So-and-so, come forward and complete the prayer with them." Then he completes the prayer with them, building upon what the first imam did, except that in reciting Surat al-Fatihah, he should recite it from the beginning so that this pillar is performed by a single imam; the rest he completes as it is.
This is the best course.
If he does not do this, by leaving without appointing someone to take his place, the ma'mums may appoint one of them to complete the prayer with them. If they do not do so, they complete it individually.
As for restarting the prayer, some scholars have said this is permissible; but there is no basis for it, because the ma'mums are excused; they do not know about the imam's ritual impurity. If they had known about the imam's impurity, they would not have prayed behind him, and they would have alerted him before he prayed with them.
As for these people who prayed five rak'ahs based on the belief that this was their obligation, they owe nothing, and they are not required to repeat the prayer, because they are excused by ignorance, and they are exercising independent legal reasoning and interpreting the evidence.And Allah the Exalted said: [al-Baqarah: 286] And the one who interprets the evidence, especially one who builds upon a principle, owes nothing. For this reason, the Prophet (peace and blessings be upon him) did not order the woman with irregular non-menstrual bleeding to make up the prayers she missed based on the belief that the irregular bleeding was menstruation. Likewise, they do not owe the prostration for forgetfulness, because they did not forget.