“Is it a bad sign when lots of people leave a church in a short period?”
You cannot judge the value of a cause by its worst day in the public square, and you cannot judge the spiritual state of a church by the number of people spilling out its doorways, never to return. A great deal more information is required to pass judgment intelligently than simply “people are leaving”. We need to understand why they are leaving, or else our conclusions will be mistaken.
Departures may be an indicator something is wrong with the shrinking church. Equally, departures may indicate serious spiritual deficiencies in those making their way to the exits.