You're correct RJ - thought I had seen a photo disappear in a merge, and it alarmed me. One of those, didn't I see ??? senior moments, possibly.
Had a spare profile I'd been saving to turn into a real person, so used it for a tester. Loaded it and another profile with photos and all made the journey to the final profile. Unsure if my being the PM of both made a difference, but next time I encounter a merge with two profile pics, will pay closer attention to what happens to them.