There is a tradition that in the Messianic era,
Our Sages teach that when the Messiah arrives the festivals will cease to be observed, but Purim will continue to be observed. The Midrash (Mishlei 9) derives this unusual conclusion from a statement in Megillat Esther, (9:28) “the memory of Purim will never cease from among their descendants.”
But in the Artscroll Machzor for Sukkot, the explanatory note on the Haftarah of the 1st day reads
this topic [Gog and Magog] is related to Succos because of the prophecy that those nations who would survive the wars would join Israel every year in celebrating the Succos festival.
The prophecy is found later in that Haftarah.
How are we to understand the nature of holidays in the Messianic era if we have so many apparently contradictory positions about which holidays will and won't exist?