According to the lawsuit itself, which would slant things in favor of the victims:
"Without warning, Green lunged at [Rangel] and struck him repeatedly in the face through the open driver-side window."
Luna saw Green beating her husband and "immediately exited" the vehicle to help him, according to Rangel and his lawyer. Green allegedly pushed her to the ground and her head struck the asphalt, leading to severe head trauma that triggered a cardiac event and caused permanent brain damage.
"Throughout this physical assault period, defendants' employees never called law enforcement or requested emergency assistance," the complaint says, alleging that police arrived only after Rangel lay injured and his wife lay unconscious on the ground.
p.s. I bolded type to emphasize it.
From the attorney's report, it appears the physical assault was over quickly. Luna got out of the car "immediately," was pushed to the ground and suffered head trauma, and it was over.
I don't see how McDonald's employees or bystanders could have reasonably anticipated this tragedy, nor does it seem at all likely that even if someone had called 911 to complain of a someone harassing people in a McDonald's parking lot, police would have arrived to this (seeming non-emergency) quickly enough to thwart the tragedy.
Harassing people in a parking lot by asking them for money is an annoyance, not a crime.
It sounds like it was over in less than a minute, start to finish, though video evidence might show otherwise.
It speaks volumes that the attorney neither says nor suggests that this was a lengthy altercation.