Q. If one was invited on Sukkos and when he arrives the family are eating in the house since at the time they started their meal it was raining, but now (when the guest arrives) it is perfectly clear, what should the guest do? Should he demand that they serve him in the sukkah, even though the Torah does not obligate them to go back to the sukkah?
A. Mishna Berura (639: 38) indeed rules that once they have started eating inside the house due to the rain, they don’t have to return to the sukka when the rain stops.
Although, the host may decide to return to the sukka in honor of his guest, the guest cannot demand he should do so. He may also instead just drink and eat fruits or foods that don’t require a sukka.
Horav Shlomo Miller’s Shlit’a opinion is that this case may be similar to travelers, that in need are exempt from eating and sleeping in the sukka, as they qualify to be called “mitztaer” or pained and hurt by having to find one.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a