Bava Metzia 76b: Rava said: If someone hired workers to dig ditches, and it rained and filled the land with water such that they were unable to dig, if the workers examined the land the day before and were aware that it might rain, he need not pay the workers. But if they did not examine the land the day before, the owner must pay the workers as much as a worker would accept to agree not to work.
בבא מציעא עו ע”ב: אמר רבא: האי מאן דאגר אגירי לרפקא, ואתא מטרא ומלייה מיא. אי סיירא לארעיה מאורתא ־ פסידא דפועלים, לא סיירא לארעיה מאורתא ־ פסידא דבעל הבית ויהיב להו כפועל בטל. פרש”י סיירא לארעא מאורתא והוליך הפועלים שם וראוה ולא הבינו שהיא לחה או שמא ירדו גשמים בלילה לית להו כלל דהא חזו אינהו גופייהו ועל מנת כן נשתכרו לו. לא סיירוה מאורתא – עליו היה לתת לב לדבר ולהודיעם אם תמצאו שדה לחה לא אתן לכם כלום, ויהיב להו כפועל בטל.
A catering company rented out a hotel in the Catskills and made a Shabbos Nachamu getaway. On Thursday afternoon there was a power outage that lasted until Shabbos, and all the food they prepared got spoiled, or could not be cooked. But the guests already arrived, so they needed something to eat for Shabbos. The catering company rushed out and bought boxes of matza and gefilte fish jars, and that was all the guests had to eat for the whole Shabbos.
Afterwards the guests took the catering company to a Din Torah and demanded their money back. The company responded that they deserved some of the payment, since they had at least given them a Shabbos retreat. The dayan opened up a Yom Kippur machzor and said, “When Yom Kippur falls on Shabbos, some say the words רצה במנוחתינו (accept our rest) and some do not. Your dispute depends on that dispute. Those who don’t refer to Yom Kippur as a day of “rest” hold that a day without eating cannot be restful. The Mishnah Berurah (582:20) paskens like this opinion. Accordingly, a Shabbos without normal, hot food is not a Shabbos, and they do not have to pay.”
Source: Rabbi Hillel David
[It sounds like the psak was that the guests do not have to pay at all. But from our Gemara we see that when an unforeseen accident cancels a job, the workers (i.e. the caterers) must be paid. Only in the case of rain, which is common, and the workers saw the property and realized that rain would make the job impossible, do they lose their wages, since they accepted that risk. But a power outage lasting a whole day is a very rare occurrence which no one expected. Seemingly then, the guests must pay at least some of the price of the getaway.]