Indeed, all your data is still present. Do not believe any messages that tell you otherwise.
The Pro1 is an A/B device. If an update fails, you should be able to go back to the other slot using fastboot. There are myriad pages on the internet about where to find the fastboot binary for your PC and how to enter fastboot on your phone. Once you are ready, simply run "fastboot --set-active=a" and reboot. If that does not work, try "fastboot --set-active=b" and reboot.
Alternatively, @claude0001 is correct. You should be able to manually install the latest nightly. I