The map will default to the enterprise you merged into one. So if it is a map of just a portion of the field, that is how it would remain and would need to be edited. You can always test this first my making a copy of a your project and do the merge there first, then you will know what the map will look like. You may want to correct the map of the Enterprise you want to keep before doing the merge. If these 2 enterprises are part of a larger field, then you can copy of the field boundary map. Edit the enterprise map and delete the portion map, (right click on map and select delete). Then right click on the mapping screen and select Paste addition, which will paste the field boundary map you got the boundary layer. Click Save and Close.