Question

Since there is no Sanhedrin, does that mean there is no halakhic ruling authority?
Does the rule that when an individual and the majority disagree, the Jewish law follows the majority, no longer apply today?
And when was that authority abolished—at the time the Mishnah was redacted?
And later, when authority was given to the sages of the Talmud, is that authority still valid today?
Or was it already in the time of Ezra the Scribe? 
By the way, I heard Dayan Rabbi Nachmanson when he was speaking about the issue of wigs. 
And about how Sephardim create a picture of reality as if the majority Sephardic opinion is that wigs are forbidden and only a head covering is permitted.
Then he shows that most Sephardic authorities, including from earlier times, say that a wig is permitted—they are talking about the wigs of the past.
And he says one can argue whether it is modest or not, and he also proves that Rabbi Ovadia Yosef says that a wig counts as head covering.
The proof is that he permitted it for a divorced woman, and he says that all the students and sons of Rabbi Ovadia—who would not disagree with him—he counts as a minority opinion. Meaning, for someone who counts majority opinions today, if it is in a situation where people do not dare disagree with that rabbi, then even if they would have thought otherwise, it is counted as an individual opinion. He also claims that people want there to be some sign that a woman is married, but that is an invention. The covering is not a sign; it is a covering of nakedness. I would add that even according to those who had the practice only to gather the hair or wear a band, in my opinion that was not because of a sign. Rather, perhaps it was a reminder not to look at hair, which is considered nakedness. And in the case of a ponytail, maybe that is because it is less attractive to look at.