Obligation to Attend the Funeral of Maran the Gaon Rabbi Gershon Edelstein

Is there an obligation to attend the funeral?

Yes, there is an obligation to attend the funeral.

The great leader of the generation is considered like a president who has passed away, and when a president dies, all activities are canceled, and synagogues and study halls are closed.

Talmud, Megillah, page 29: "We cancel Torah study for the funeral procession and for the bride's entrance. It was said about Rabbi Yehuda bar Ilai that he would cancel Torah study for the funeral procession and for the bride's entrance. In what case are we speaking? When there are not enough people, but if there are enough, we do not cancel. And how many are needed? Rav Shmuel bar Inya said in the name of Rav: twelve thousand men and six thousand trumpets. And some say: twelve thousand men, and among them six thousand trumpets. Ulla said: like when men stand from Avula to Sikra. Rav Sheshet said: as it was given, so it is taken. Just as it was given with six hundred thousand, so it is taken with six hundred thousand. This applies to those who read and repeat, but for those who teach others, there is no limit." Thus ruled the Shulchan Aruch, Yoreh De'ah, laws of mourning, chapter 361: "We cancel Torah study for the funeral procession. For those who teach others, there is no limit, even if there are several thousand with him, we cancel for him." And in Moed Katan, page 22, side 2: "When a president dies, all study halls are canceled." And it is written in Yoreh De'ah, chapter 374, that the great leader of the generation is considered like a president.

And the Shach wrote there, section 1: "It is an obligation to cancel, as agreed by the decisors."