Hoist by my own petard: I just now realized the only way to login to my old Flickr account is via the Yahoo address I deleted last week. I was able to somehow get into it because my browser thought I was still logged into that email and downloaded the few things I had on there that weren’t saved elsewhere.
I should download all my dad’s stuff as well. Not sure what Yahoo does with the Flickr accounts of people who are deceased. But it’s been 3 years and it’s all still there, so maybe it’s safe for now.