Imagine the behaviour of your popular community manager becomes intolerable in the office
After several warnings, you decide to remove him/her.
How would you do it without upsetting the community?
If your answer is to explain to 1m+ people why an employee was fired, consider the morality and legality of that.
Now imagine that employee tells members they don't know why they were fired and their friends in the community should protest against their removal.
The solution isn't for the company to publicly reveal why they terminated an employee, nor to force all employees to use a 'brand' account so you don't have any 'named' employees'.
And the solution is certainly not to overlook other areas of an employee's work because they're popular with the community.
At this late stage, there aren't any easy solutions.
Far better right now to ensure you have more than one star from your company participating in the community. Far better, if an employee does need to be released, to have someone or something more popular to replace them.