If Moshiach should appear during the days between Rosh Hashana and Yom Kippur, it is conceivable that we will eat and drink on Yom Kippur if it falls during the seven-day dedication of the Third Holy Temple. This was the case with the First Temple, whose dedication began on the eighth of Tishrei, and the people of that time ate and drank on Yom Kippur.
(Sefer HaSichot of the Rebbe, 5749)