This might not relate to the NSX as different timing belt materials might be involved.
I just changed the timing belt, tensioner and water pump on my 1995 civic with 350000 kilometers on it (not miles). I think RON98 hit the nail on the head here. I would have never changed my belt however my water pump started leaking slightly. I didn't want to get stranded so I changed everything ($88 for the timing belt, tensioner and water pump with a $7 core return....oh ya). The timing belt I pulled off was an original Honda belt and you could still see the writing on the face of it but I couldn't see a date or time stamp on it unfortunately. I'm not sure if anyone has ever changed the belt on this car but here is what the belt looked like. Note that I did not "break" the creases; this is what the belt was like naturally and EVERY single tooth was like this. As RON98 said if the water pump or tensioner seized up I have no doubt in my mind that teeth would get stripped off of the belt. I doubt the belt would even break. I tried to break the belt by holding it on the ground with my foot and pulling up towards my chest with two hands and nothing.
Your timing belt might have had some amount of life left in it but timing belts have broken without being precipitated by a water pump failure both before 7 years and before 90k miles on an NSX.
And second, if one's water pump goes before the timing belt (at least in an NSX) you're going to be stranded all right--stranded with a broken motor.
By the time your water pump begins leaking it has passed the point where it could seize spontaneously and destroy the TB within seconds.
Waiting for a leaky water pump is very risky since the TB could break anyway and if the WP fails the TB could fail.