The first person I thought of was Victoria Wood, she was such a talent and always seemed so normal and decent. She died too young, I'd bring her back so she could live on enjoying her life and entertaining us.
Selfishly for me, Richard Briers, just because I adored him.
But if I had to choose one, it would be Alan Turing. So he'd know that his genius - in the truest sense of the word - was recognised, and we could pay tribute to the man that arguably saved the world from tyranny in 1941.