MacBook Pro is frozen on blank screen during high sierra update

Yes, all the data on the drive is erased. If you cannot backup then you can try the following. But if it does not work then you will need to do the full erase and install.

Reinstall El Capitan or Later Without Erasing Drive

Please be sure you back up.

1. Restart the computer. Immediately after the chime hold down the Command and R keys until the Utility Menu appears.
2. Select Disk Utility and click on the Continue button.
3. Select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid icon in the toolbar. Wait until the Done button activates, then click on it.
5. Quit Disk Utility and return to the Utility Menu.
6. Select Reinstall OS X and click on the Continue button.

Also, see this User Tip: Basic Steps for Upgrading OS X.

Force shutdown by holding down the Power button until the computer turns off. Wait 30 seconds and restart the computer. See if the installation picks up and continues. If it fails to do so, then follow this:

Install El Capitan or Later from Scratch

Backup if possible before continuing.

1. Restart the computer. Immediately after the chime hold down the CommandandRkeys until the Apple logo appears. When the Utility Menu appears:
2. Select Disk Utility from the Utility Menu and click on Continue button.
3. When Disk Utility loads select the volume (indented entry, usually Macintosh HD) from the Device list.
4. Click on the Erase icon in Disk Utility's main window. A panel will drop down.
5. Set the Format type to Mac OS Extended (Journaled.)
6. Click on the Apply button, then wait for the Done button to activate and click on it.
7. Quit Disk Utility and return to the Utility Menu.
8. Select Reinstall OS X and click on the Continue button.

Hi there, I possessed that issue a while back, to resolve this, you must reinstall your macOS. To do so either call Apple Support or follow these directions:

https://support.apple.com/en-ca/HT204904