Optics don't know about pixels. To a first approximation, they are continuous. Whatever discretization happens after that, it's not relevant to the optics in any way. A sharp lens can greatly outresolve a low-resolution sensor; the bottleneck is the sensor in that case. Conversely, a high-resolution sensor may not be of much use if the lens is soft - but in this case you can at least in theory use deconvolution to recover detail if you know a good approximation of the PSF of the lens. This is not uncommon when working with scientific instruments, actually, but pretty rare in the case of consumer photography equipment.

No, because a pixel is not a point. Even if not-perfect optics blur the point a bit, it can still be one pixel or less. Ideal optics might be able to focus the light much smaller than one pixel, but that won't change the resulting image because the pixel sensor will pick up the same amount of light.

"A Pixel Is Not A Little Square"

http://alvyray.com/Memos/CG/Microsoft/6_pixel.pdf

And elementary photosensitive units (whether silver halide grains on photographic film, individual sensor elements in a CMOS or CCD image sensor, or photoreceptive cells in a mammalian retina) are not points. They have a nonzero area and turn photons into signal irrespective of where they hit. That article, while very informative, is not relevant. Sensels are not pixels.