to fade a scene out in the editor screen you need to set the scene fade out in the editor box top ribbon, right click and tick scene fade out.
However this will now fade all chanels to zero over a specified time.
If you want to fade shutters / dimmers only I suggest you create a new scene in your with all shutters set to 1, this will now force all chanels to dmx level 1, now create a next scene with group release. So within your group at the end the first new scene will fade all shutters to a level of 1. this then next autos to the next scene with the same level 1 scene in it , or the lights will flash back to a previous level. this final scene is auto release and group release.
Now you have the perfect fade out.
Music sets the mood Lighting sets the ambience