High Sierra - The path /System/Installation/Packages/OSInstall.mpkg appears to be missing or damaged

Same error happened to me when I received an update from 10.13.1 to 10.13.2.

If you boot with shift button pressed, you will be able to enter safe mode and try to download and reinstall an update. It did not help to me so I booted holding Option key and chosen regular Mac HD (not an update volume). Booted to my Mac without safe mode and tried to reinstall this update. Somehow it worked out in several reboots.

The easiest solution is the one by commenter Michael Buen. It has worked on 20 Macs I've seen have this issue.

Apple Menu -> Select Startup Disk -> Restart (after clicking your boot drive) resolves the issue, at least temporarily. This can be done at the error screen, by clicking on some empty space in the grey message box to get the apple menu bar to appear. You can also get to this "Select Startup Disk" menu option by starting up the Mac in recovery mode (cmd+r) or internet recovery (cmd+optn+r). If you use FileVault encryption, you'll need to enter your user password to unlock the drive.

Re-installing MacOS on top if itself also solves the problem, but takes more time. Internet Recovery (cmd+optn+r) and a MacOS bootable USB installer disk both work and in theory do not delete any personal data.

I've seen it recur more than once on the same computer. Updating to the latest point update for High Sierra (10.3.3 Supplemental) might be advisable, but does not guarantee a resolution.