Thom,
How could he accept?
His opponents, even if only a few show up, are Gelugpa Geshes, brought up in the ancient Indian Buddhist logic of the two treasures Dignaga and Dharmakiirti, and children of the Tibetan yogi logicians, Je Tsong Khapa and his sons ... who would dare be their opponent?
The Dalai Lama is a debater himself, he knows beforehand that he is defeated. He will never accept.
Forget Tibetan tribes. In ancient India, when religion was not so much a matter of labels as it was of proven wisdom, Masters debated among themselves ... at the end of the debate the disciples of the loser became automatically disciples of the winner.
.....