...The F-16 cockpit canopy/with survival cell has been used in Unlimited Hydroplane racing for past 25 years without any fatalites.
Unlimited hydros don't often crash into fence posts.
The curvature of its canopy is intended to deflect the force of impact with water, not to absorb it. The very nature of curvature reduces structural integrity, which is why engineers regard the triangle and not the circle as the strongest of 2-dimensional shapes. Upon striking a solid object, a curved canopy concentrates the force of impact onto a small area, which promotes failure.
Wheldon's car was leading with its cockpit when it struck the post. That's 1600 lbs+ striking an area the width of that post with a force of more than 400,000 lbs (180 metric tonnes+). GE Lexan 101 has a "modulus of rupture" of a bit over 14,000 psi (~980 bar). Even given that portions of the car struck the catch fence first and had begun to deaccelerate, I think it highly likely any canopy would have failed as well, particularly a curved one.
Not to put too fine an edge on it but Wheldon died because his skull experienced such high deaccelerative forces, his brain could not endure the collision against it. Those deaccelerative forces occurred in three axes, and the brain is particularly susceptible to injury by rotational force (most pugilistic "knock-outs," point of fact, are the result of high centripetal loads, not linear force). I've read no credible analysis to date to indicate Wheldon might have -- just
might have, not
would have -- survived if his car had been equipped with a canopy.