So, where is the bug and where is your issue on how the issue was solved? Systemd just rotates on corruption, and the issue is resolved. What do you want? That systemd magically fixes the corruption, that systemd can go back in time and retrieve the log message? There is absolutely nothing that any computer can do on file corruption, or on sudden power loss.
"The next question seems obvious to me though - how do we avoid that in the future?"
Have better hardware, have a RAID, transfer the log messages over the network, have a UPS on your computer, invent a time machine.