I have seen a single (1) mention of View port background images disappearing when the .blend file is saved and reopened. However...the answers are not relative to what I am experiencing.
I go through the trouble of setting up four images (top, side, front, back) and then pack these images using
External Data > Pack all into .blend and then I save the .blend.
I save the file, open it back up, and the background images are all gone. Open up properties panel, look to see background images check box is unchecked, click add image, and choosing the open drop-down arrow...the data paths still show the list of images (packed into a specific folder textures). They are still there, the data set is intact.
Why is It that I have to set this up each and every time I open the file. It seems like earlier versions <2.76B saved the images and saved the file with the background images check box checked without the need to set this up each time the file is reopened. This is getting very frustrating due to the fact that a few of the background images mus be set up using Blender's rotate, scale and move tools to align the background image up with the model I have already fabricated.