I don't believe Yuki-chan sensei (that's her name in the credits, ユキちゃん先生) died in the Itomori Accident. In the universe where Mitsuha had foreseen the disaster, she recruited the help of her friends, Teshigawara and Sayaka, to try to obviate casualties. Sayaka broadcasted to the townspeople to evacuate to Itomori High School, but was shortly stopped by the arriving school staff, which included Yuki-chan sensei.
This means that Yuki-chan sensei was at or near the school, a place of safety, by around 7:42 pm, one hour before Comet Tiamat would strike. There is little sign that she would head to the festival place within one hour, as she was not dressed in yukata (most women were dressed in yukata at the festival). She would most likely stay for after-school duty for the remaining time.
And to refute Anon's comment, in Kotonoha no Niwa, Yukino actually said at the start of September 2013 that she would go back to her hometown in Shikoku in a week. Moreover, she was later seen teaching a class in Shikoku, and even wrote a letter to Takao dated February 3, 2014. She was definitely not dead, and Takao didn't make any altar for Yukino. All these details entail that Kimi no Na wa and Kotonoha no Niwa couldn't possibly be set in the same universe, even though Yukari Yukino appeared in both movies.