Well, technically it's the Ashkenazi pronunciation of a Hebrew word. Some Jews regularly use this pronunciation in all religious contexts. But you're right, Yiddish does have a big vocabulary of Hebrew words, and this is one of them.
Many Jews use these Hebrew/Yiddish/Yinglish words in English sentences too: you can't tie down a word and say it only belongs to one language.
Judaism will never die! There will always be Jews observing the Sabbath. In the 01/01/2000 publication of the New York Times they had the front cover of the years 1900, 2000, and 2100, and the latter had the candle lighting time on it, because as the non-Jewish editor said, even when the moon would be found in the Tlantic there will still be Jews lighting Shabbat candles
Throughout this time lesson I've noticed that the days of the week are never pluralized (Saturdays, Mondays, etc.) even in sentences were it seems like they should be. Ex: "He wears this shirt on Monday." Does this refer to only that one Monday, or can it be understood as on Mondays in general?