Sorry for my fixation on Tanuro Shel Achnai. The Gemmorah says that at the time of the incident R' Gamliel (the Nassi) was in the high seas (B"M 59b):
ואף ר"ג היה בא בספינה. עמד עליו נחשול לטבעו וכו
And even Rabban Gamliel, the Nasi of the Sanhedrin at Yavne, the head of the Sages was coming on a boat at the time, and a large wave swelled over him, etc
Both Talmuds and Most interpreters understand the Machlokes as אחרי רבים להטות - R"E's refusal of following the majority. However, this rule is only applicable to a valid [high] court.
How an obligating Halacha can be ruled in a court without the Nassi present?