That cannot be answered with certianty since it depends on your driving habits greatly. But with just everyday driving (no hard launches) it could last up to 60,000 miles. But with hard launches and trips to the track you could burn it up in 5,000 miles or even sooner.
The above post is right on the money. It totally depends on your driving habits. Not only will harder driving styles reduce clutch life, but poor driving habits as well. Many people rest their left foot on the clutch petal and press it in a little with out knowing it.--DEPENDING on where (at what point) your clutch enguages, you can actually cause your clutch to slip and burn during normal driving.
I'd say the average Clutch on a stock 03/04 cobra will last 50-75K miles. This would include some "fun" drving as well.