That is a good question, and when the site started now almost 20 years ago, possibly nobody considered that.
Now this site comes under British copyright laws, and as I am not British I am probably less qualified to talk about it.
What I could say is that normal practice seems to be that the photos stay on the site, where sometimes a note has been attached that the photographer deceased, but not always.
I assume that the correct policy is to keep the images on site, until people dealing with the estate request these to be taken off, but I welcome any comment from members who have been dealing with this issue in the past.