I would like to review literature on the following question:

"How to assess whether a company is losing customers due to internal
customer service and process or due to an economic downturn or
industry shrinking" - how to measure, what to measure

First test I would make are:
Are there any internal customers? Do the employees of the company
recommend the company's product to their family and friends. If not it
means the employees are going through the motions but do not believe
in the product or the longlevity of the company due to management.
Those who have recommended the product to family and friends will they
continue to do it.