When has a Pastor stayed too long?

In the Church of God, how is it determined that it's time for a Pastoral change? Is it the declining health of the Pastor? Is it declining church attendance? Is there a limit to the ineffectiveness of the Pastor to lead before the AB drops the hammer? If another church located just a few miles away suddenly starts seeing an influx of the Pastor's members, does that mean he has stayed too long? Is there usually an understanding by the Pastor and the AB that it's time? I'm really interested in how this plays out in the CoG.