Actually, [filing a civil suit] old marksman already addressed this, that evidence IS required.
I think you mis-interpreted either his or my post. No evidence is required to FILE a civil suit. You could file suit against me today for any number of civil offenses even having never met me and have zero evidence. You may not get an ethical lawyer to help you, or you might. Or you could represent yourself. Even without evidence, you file suit and I'd have to answer to your charges, real, imagined, supported or not supported. Evidence would surely be required in most cases to PROVE your side of the story, but not always.
"I burned my thighs when the hot McDonalds coffee spilled on it". "I opened your can of olives and found a mouse". "While I was in your jail serving my sentence, your deputies made fun of me when I prayed" - are all suits that have been filed with no evidence. They may not prevail, but they could file.
is it always wiser to retreat, if possible?
Yes. Always. 100% of the time.
I would have to think that a retreat, if verifiable, would make the shooter look better? Am I right?
Consider shifting focus from "Shooter looking better" or "Getting away with it" to "Maintaining my sanity". Carrying a deadly weapon shifts (should shift) your thinking NOT toward "I'm safe now to go into that situation" to "I have to now be xtra careful not to go into that situation because it might result in the 2nd worst thing that could happen in the world, I kill someone".
Sgt Lumpy