I'm sure this has been asked and answered many times already, so I apologize in advance for asking again.
I have no power on my house and 4 characters in play including Beric Dondarrion when my opponent plays Wildfire Assault. I choose the other 3 characters and let the Wildfire resolve...
My understanding of the rules is that all 4 of my characters would live since Beric cannot be killed. Despite the "cannot be saved" wording on Wildfire, since Beric CBK I am not required to try to save him. And since I was not required to choose Beric to be killed (Wildfire make you chose the other characters) I am not breaking any rules about selecting a CBK character as the target of a kill.
Can someone please verify how this works? Thanks a lot!

Couldn't have said it better myself. You got everything right.

i think you must choose Beric as one of the three.

Just like the rats.

Uncle Joker said:

There is nothing requiring you to choose Beric. If you don't choose Beric he won't be killed because he cannot be killed. Wildfire Assault's cannot be saved condition only applies to killed characters. Beric is CBK (when you have no power on your House card), so if you didn't choose him as one of your three characters it doesn't matter. Either way, he's not killed because he can't be.

Uncle Joker said:

You don't have to choose Beric or the rats as one of your 3 for Wildfire - which will then fail to kill them.