ouch. that why you don't try something like this from bannerbomb.
If you the firmware downgrader fails and you have homebrew channel installed you can just go back to the HBC, start firmware downgrader again and try once more.
If you try it from bannerbomb it will spit you out into the system menu and you are bricked... You should try savemii free to see if your rescue menu still works. If it does there is some hope to fix the Wii with a game-disc.