Now Rabbi Slifkin has stooped to inventing sources in support of his thesis. R’ Yosef Caro does not say that "Chazal could indeed be mistaken; nevertheless, we never dispute their rulings." What he says is that although normally a latter Beis Din may dispute the halachic rulings of a former Beis Din, the chasimas haMishana and chasimas haTalmud are apparent exceptions to this rule. And he certainly does not say that matters of life and death are exempt from the "canonization" of the Talmud. Rabbi Slifkin’s blatant misrepresentation of the sources reveals the depth of his prejudice in these matters.
Yesterday, I noted how Chasam Sofer was of the view that the Sanhedrin may be mistaken in their rulings, and yet they must be obeyed, due to the importance of a centralized rabbinic authority. In this, he was following the approach of Sefer HaChinnuch (and, arguably, some others). Rav Yosef Caro, as explained by Rabbi Shlomo Fisher, takes the same approach to Chazal. Chazal could indeed be mistaken; nevertheless, we never dispute their rulings. This is because the Jewish People canonized the Gemara; we accept its binding authority, regardless of whether or not Chazal were correct. (Cases involving matters of life and death are an exception to this, as discussed previously).
(For Rabbi Caro's treatment of this topic, please see Kesef Mishnah to Rambam Hil. Mamrim 2:1)