Assuming Flexnet is being used with MATLAB on the server:
Once the connection to the Server is lost, the interactive MATLAB sessions issue 10 warnings about a loss of connection to the server. The warnings only appear when hitting the return key in the MATLAB command window. Subsequent warnings will be issued after another one of these interactions(hitting the return key) but only if it has been more than 2 minutes since the previous warning.
After 10 warnings MATLAB will exit within 15 minutes. A running MATLAB session will never exit unless the user is actively using MATLAB. And new licenses cannot be checked out from the license server.