This one is tough. Mark Hollis recently passed, and that was difficult to process but in the musical sense he was already gone, having left a near-perfect legacy of forward-thinking avant-pop that to most people's minds invented post-rock.
Scott Walker on the other hand, despite his age, was still fairly prolific, especially considering his attention to craft and detail.
I can think of at least 4 moments where he defied expectations: Quitting teen idoldom to write music, Scott 4, his songs on Nite Flights, and Climate of Hunter, which really established the rest of his career. There was nothing else on earth like them. There was nobody on earth like him. And there never will be.