Why 640x480?
Does anyone actually play in that resolution? Is the graphics better (meaning, is everything clearer)?
By the way, it might be possible to implement some kind of emergency stop mechanism if you decide not to continue digging for a hero or if the hero stubbornly can't be found. Otherwise, you have to go into the processes and quickly stop the heroes before the cursor gets stuck in the digging animation again. For example, the digging process for 3 heroes could be stopped when the program window is restored.