In Lumerical FDTD, how do I retrieve my simulation file when my license is disconnected or my computer goes to sleep?

You can avoid this issue by selecting FDTD-Edit Object----Advanced option -- check the box on check point option before you begin a simulation. After that, enter the interval time you wish to save your results.  We select 2 minutes here.

Select resume as shown in this picture if you want to start from the previous simulation time.