Would a CT Scan without contrast show signs of an unruptured anyresum?

Probably not, in that cirstance. Moreover, if there was any significant risk of it being a "warning leak," he'd have insisted on a lumbar puncture (spinal tap) right then. Apparently something said to him but not in your post here made him confident that you needn't worry. I don't see an MRA in your future (and that, rather than MRI, is what you'd be thinking).