The solution might take several forms but maybe you should project your images on nurbs planes, thats how I would work around it.
You can actually set your workinng units in maya to inches, then open your blueprint in photoshop to determine it's exact dimensions in inches. Then go back to maya and create a nurbs plane with those same dimensions. Then you can simply apply the blueprint to the nurbs plane. Then I would add the plane to a new layer and set it as a reference layer to avoid it being accidently selected.
This is how I set up my image planes in maya.
As for your problem, the reason why I think that the image plane is dissapearing is that the image plane is attached to the top view camera. If you make the camera part of your selection then you shouldnt have that problem, but because it is a camera attribute that is harder than just using an nurbs plane.
But if you want to do it your way:
1)select the faces you want
2)open windows->outliner and ctrl-select the top camera so that you have both the face AND the camera selected. Then just go to isolate select again and the image plane wont dissappear.
