I'd still be considering mileage on the engine as a key part of my decision. Low annual mileage the petrol would win, simply as I don't see the diesel being the best engine (long term) for short trips and low mileage use.
But if driving more miles and particularly if in lots of traffic, where I'd be continuously working the engine and gearbox, I'd have the diesel.
I've been an advocate of riding the "torque wave" of a diesel for years, long before most would even dare look at a diesel car. To be honest, for my current driving, I'm not missing the diesel 'shove' at all. But I'm sure I would miss it, if driving every day in traffic.
So for me it isn't a fuel cost issue.