No, the MBA won't kill the iPad: there is a tremendous mass appeal for the iPad that extends beyond Mac owners and potential Mac owners. Windows netbooks and laptops certainly haven't killed the iPad among those who are outside of Apple's ecosystem. The MBA might kill the iPad for individuals like us who want some sort of portable Mac and find that it fits our needs better than an iPad, but for the zillions of people out there who have no desire to own a Mac, an iPad is a viable ultra mobile computing device.
I love my new MBA, but the iPad is still my "go to" device when I want to do something computer-ish that doesn't require a laptop: it's just so handy. The two devices complement each other nicely.