The Network License Manager can be configured to reclaim a license when a client workstation is idle for longer than a defined time-out period, or the connection with the workstation is lost.
For details please check the solution here.
The debug log file can be examined to determine if a license has been reclaimed. When a license has been reclaimed, the debug log file will contain a line similar to:
10:11 (adskflex) IN feature_code user_name@host_name (INACTIVE)