Beautifully written story. They're both very IC - yet likeable in ways they're not in canon. More shades of grey, rather than JKR's occasional too-black-and-white, I guess.
Some great lines: But he detested unpleasantness, and last night had been full of it. What an utterly Slughorn way to describe the Battle of Hogwarts.
Horace's mind flashed an image of Cornelius in days gone by: burgundy robes, twinkling eyes, a knowing smile and a glass of brandy crooked in his right hand. Such a vivid image of the old Cornelius.
"They...they so very much don't look after you in there, you see." Poor Cornelius.
and and Cornelius glanced at him with a hint of his old sharpness. "I doubt that, somehow. Invalids are terribly boring creatures. Always hated 'em, myself." In a way, they're made for each other.