As you know, when simulating a GridFluidDomain with the displacement maps to Yes, the maps are calculated in simulation time and they can’t be exported after simulating.
So, if you forget to check the checkbox to export the Displacement maps in the Export Central, the maps won’t be saved. But don’t worry, because it is not necessary to simulate the original scene again to generate the displacement maps. You just should duplicate the original GridFluidDomain01 with the same settings and go down the resolution value for the new GFD02 duplicated to 1 or 10. The new duplicated GFD02 must be in Active mode. Make sure you have the Displacement map checkbox checked in the Export Central for this GFD. Even you can change the name for the maps textures in the Export Central to GridFluidDomain01. Next, put inactive all nodes except the duplicated GFD and simulate. Now, the displacement maps will be exported and you can apply to the original GridFluidDomain.