If less than 40% of your customers say they would be "very disappointed" if they could no longer use your product, your team is still looking for product-market fit.
Survey questions
These are the questions you should ask your customers/users. The answer to the first question is the metric you should be tracking over time to see if your product has reached product-market fit.
How would you feel if you could no longer use the product?
Where do you get the most value out of our product?
What could we do to improve our product?
What areas don’t you see benefits in?
Are there any problems our solution isn’t solving?
For an end-to-end template on implementing a survey and seeing the results, check out Rahul Vohra's published doc on how he tracked product-market fit for Superhuman: