The power in my house went off for 1 second as I was gaming.
After the computer restarted my character has been erased from my account, all my other characters are still there.
I was playing with that character just as the power shortage happened and turned off my PC.
How did it delete the entire toon and didn’t do a rollback to some previous save state?
Its possible the character is still there but the offline save file is corrupted.
Do you use Steam cloud sync? If so, it might be in the save data on Steam (or if it was a brand new character, it might not).
You can try to find the save file yourself and see if it is busted. Lastepochtools.com build planner has an import function which tells you the save locations.