You will still be graded for this and I think if you don't turn up (without a medical reason or otherwise), they will mark you zero. This will be worse than whatever you get if you go in and at least attempt the exam.
University's will see this. However, they are more likely to notice a 0 than something higher, but not as high as your other grades, because from my experience, if they see the A-levels you continue with are all A's and you do well in them at the end, they will not focus on one lower result. But they may not overlook a zero.
My advice would be to go and give it your best shot :-)