Sarah - funny thing, I went for about a month with only one contact lens, until I finally dragged my butt into the optometrist's office to order a replacement. Your brain does get used to it pretty quickly.
I haven't tried diving one-eyed though, and don't know if I'd be comfortable doing so. Depending on how strong your prescription is, I'd be fairly disconcerted if my only contact popped out underwater and I couldn't see my gauges or anything. It'd be the equivalent of being maskless.
I usually wear glasses but the vis in monterey is so good.... that it doesnt matter that I dont dive with them .