Indeed. If Thatcher can bring herself to attend Heath's, then the least Blair could do is to attend the funeral of somebody who, whatever your views on his politics, was the formost parliamentarian of his generation and a major figure within the Labour Party.
I was no fan of Robin Cook. He always struck me as smarmy and a trifle obnoxious. But I'll give him this: if you are a Scot,the best way to go out is sudden death while hiking in the beautiful Highlands. As a departure, it beats most of the alternatives. So RIP and best of luck in the matter of Pascal's Wager. As for Blair's attendance at the funeral, I suspect that Cook doesn't care so why should I.