In this paper, we study the behavioral communication patterns of employees in the last few months before they quit their company. Our study is based on Slack communication metadata from two technology companies. We analyse the communication patterns of terminated employees in the last 15 months before they left the organisation. We use different metrics such as the volume of messages sent, the activity in different channels, the average range of communication, and the number of collaborators over time. We also compare the behavior of the employees who are about to quit versus the company average in the same time period. We discover that there is a clear communication pattern for employees who quit with a pronounced decrease of engagement in the last 5 to 6 months before they left. We then build a machine learning model to predict if an employee is at risk of leaving the company within the next 6 months.