(1) Control anger. Getting clipped by a car is no laughing matter, but getting into a shouting match and kicking someone's car is escalation, even if you feel it was emotionally justifiable. An armed person needs to seek to de-escalate confrontations. It is part of the discipline of carrying.
(2) Notify the police at the earliest opportunity after being assaulted the first time. If your relatives and friends felt they needed to end the first incident before making a call to 911, that is certainly understandable, but there is absolutely no reason not to report such a serious incident immediately upon its conclusion.
(3) If the police response was even marginally adequate, the second incident shouldn't have happened. If it was not, the employer should have been notified and the job site should have been made more secure before work continued. I employ a few people, and I feel responsible for them. Security and self-defense measures are in place. The safety of my employees takes precedence over any and all issues of finance and material possessions.
The use of a firearm is a last resort, but one that all free people have a right to employ when needed. Only someone who was there could say how big a threat was present during and immediately after the worker was hit by a car. But if a firearm was brought in to play when the thugs returned, it would be much harder to explain and defend in the absence of a 911 call than if law enforcement had been notified. The lack of involvement of law enforcement agencies is a big problem in the way the situation was presented by the OP.