Hello there @Binky_Destroyer / Mat! Welcome to the forums
I'm sorry to hear that you have lost your level 100 hardcore character following a crash. Thank you for taking the time to share your report with us.
Please note that we are unable to restore hardcore characters once they have died in-game. I understand that this may not be the answer you were hoping for, and apologise for any disappointment that has been caused. You can read more about hardcore mode in this blog post.
CE-34878-0 is a console error generated by the PlayStation console. You can read more about this error, as well as some further troubleshooting steps, in this PlayStation support article. If you are encountering this error frequently, I would recommend contacting PlayStation Support for further assistance.