I’ve never been strict about using correct grammar in speech, especially when it’s in informal settings like in everyday conversation. It’s a bit of that ‘it’s okay as long as it’s understandable’ attitude that quite a few of us have, since we’re throwing so many languages into the mix and it’s impossible to set any standard of correctness anyway. However, it shouldn’t carry over into formal writing. Even if you’re writing a short story or a novel, it should only make an appearance in dialogue.
This is understandable to almost anyone, especially when said with the right intonation:
Why Susan didn’t go with her family? ❌
Or the slightly worse offender:
Why Susan not go with her family? ❌
It’s very Manglish and an easy shortcut. I use that form pretty consistently in daily speech. Think about it—you probably do, too. The question word, then straight to the subject instead of having an auxiliary verb in between: Where we going for lunch today? What you working on right now? Why you not joining us? But none of that is grammatically correct and shouldn’t be used in writing.
The correct way to form the question would be:
Why didn’t Susan go with her family? ✅
Or if you need to be really formal and not have contractions, then:
Why did Susan not go with her family? ✅
Just because the question is phrased in the negative (what she didn’t do instead of what she did), it doesn’t mean that it doesn’t follow the usual pattern of question word + auxiliary verb + subject (and the rest of the question).
Phrase your questions correctly:
Why didn’t Susan go with her family? Who is Susan anyway? Where did her family go? How did they get there? When will Susan join them?
Poor Susan. So many questions to contemplate.