They stay as long as you don't move where they are located on your hard drive. I'll make it clearer, I tend to confuse. I have all my jpgs in a folder called marriages, sorted by family. I file everythinbg related to an unmarried child in the parents folder. If I discover a spouse, the child gets its own folder and I move the photos, docs etc to the child's marriage folder. Now they are no longer connected. The photos still use the path to the parents' folder. I go to any photo for child, point it to the correct path and all photos are automatically linked. You can also run a report and the program will show you all unlinked photos.
It's the linking I love. Family Tree Maker used to, maybe still does, add the photo to the FTM file and bloat the file.
Download the free Legacy and give it a spin. I believe the free version is somewhat limited to what it can do wilth photos.