If an employee leaves your company and you deactivate the account, incoming calls to the former employee's Sell phone number will fail.
The risk is that customers or accounts owned by that outgoing/former employee will continue to call that Sell phone number, but will not get through (as their is no voicemail, no call transfer/forwarding, no direction as to what action the customer can take to get in touch with your business).
There seems to be no way to manage incoming calls for outgoing/former employees other than keeping those user accounts active (not optimal) and having existing employees manage the incoming calls.
