I can’t get the system back via Recovery Mode/Reinstall macOS. That only gets me back to the progress bar at 100% (I tried that).
So, what if I boot from a thumbdrive with High Sierra beta 4, can I reinstall macOS from that, i.e. on top of the current beta 4 / beta 5 installation, without loosing all?
Not a bad idea.. give it a shot and let us know lol