Non-destructive healing allows you to "heal" the pixels of an image using a separate, dedicated layer so that you can undo or modify your changes at a later point in time. In (Photoshop and) GIMP, this essentially works by performing the heal on an empty layer using the Sample Merged option which allows you to perform the heal as if all the layers were merged together. While this works fine with the clone function, it is broken for healing in GIMP (2.8) due to this bug :(
Rather than use images with transparencies, it is often preferable to replace transparent pixels with a suitable background colour.
In ACDSee 4, the background colour of transparent PNG files (or any other image file that supports transparency) is by default set to black. There is no immediately apparent option whereby you can change this colour and then save the file as a JPG or similar. After some asking around, I was told that while it is possible to customise this colour, it's a bit of a pain. Here's how:
If this isn't way cool, I don't know what is.