Hi,
I had the same issue with MacOS HighSierra 10.13.1. When I try to restart or shutdown my iMac, the menu bar disappeared, but nothing else happened. So I was forced to press power button for shutdown. This behavior also prevented me from installing the update to HighSierra 10.13.2, because a proper restart is necessary for installing a new update. But I figured out a way to come around this issue.
That's what I did:
1) backup your data
2) on update page of App Store, press "install" to download update for HighSierra 10.13.2
3) press "restart"
-> now menu bar disappears, but nothing else happens...
4) start any other app, e.g. mail
-> menu bar appears again
5) in menu bar choose Apple Logo -> Force Quit...
6) select entry for Finder and press "relaunch"
-> iMac restarts and installs update
In case you get stucked during update on "grey screen" be patient... However, if for a long while really nothing happens, press power button to force shutdown. Restart your iMac. Now, installation shall continue and finish without further issues.
After HighSierra 10.13.2 was installed successfully, also the reported issue with hanging restart / shutdown did not occur anymore.
At least, that's how it worked for me. Good luck!