macOS partition not showing up after High Sierra update
Try System Preferences -> Startup Disk -> macOS. I updated Sierra on my MBP (late 2016) and was unable to boot into Boot Camp. Fixed over the phone with Apple, but then I was unable to boot into macOS. They fixed that at the Apple store today using the above commands.

If you want to boot into Windows directly, just hold down the "option" key while you press power on button. This saves you from having to log in to macOS and then restarting while holding down the option key.