Is there a word for when the situation returns to normal after chaos?
Solution 1:
“All clear”
This is the phrase one might employ in Britain, especially if one is of the older generation. It was the term for the siren used in World War II after an air raid (although it predates this) and has featured in many movies and TV dramas portraying that period. It became a noun phrase “the all clear”, as this BBC page documents.
See also the Wikipedia entry.
Solution 2:
You could use 'crisis averted', however it is not a one word. Urban dictionary suggests: Pheww https://www.urbandictionary.com/define.php?term=Pheww ;)