in short, if I were in a crowded fast food place or small business(check cashing shop, dry cleaner, store, etc). I'd get to a safe location, contact 911/local LE then give a detailed description of the events.
Unless I was directly assaulted or a bystander was hurt or the subject(s) made a hostile move, I'd keep my concealed weapon(s) secured.
As a licensed security officer, I can tell you openly that many confrontations & street fights are fluid, chaotic and can you can be over-run quickly.
I 100% would not rely on any of the other patrons/citizens to help you or be honest with the local PD either. These "lie-witnesses"
will watch you draw a sidearm then freak the $%&* out!
CCTV & security systems are a great benefit. I'd also keep all your licenses/records/qualifications up to date if possible so any prosecutor/media reporter/criminal investigator can't twist your words or dispute your documented proof of carrying a loaded firearm concealed or using force if needed.
About 6mo ago, a local NBC station ran a media item about 2 homeless men who assisted a sworn deputy as he fought a subject in a fast food restaurant. The newscasters critized the other patrons for not helping. I disagree with the news anchors. I'm not going to jump into a active fight when uniformed LE officer with 4-5 weapons is rolling around a crowded area.
There are a lot of risk factors and legal issues involved in a high stress event like that. it's better to be a good witness if you are not a sworn LE officer sometimes.