Even if this happened in a Concealed Carry state you can bet that the Burger King would have a policy of no employee may bring a fire arm to work policy.
Most employers do not want the liability of armed employees.
Unfortunately there has not been any civil liability lawsuit that I have seen against an employer that forbade employees in high risk positions to carry that subsequently were killed while forcibly unarmed.
Perhaps someday a truly outrageous case will come to light and that will be remedied but I won’t hold my breath. It would take Gun Owners of America or some other similar group to take such a case.
Too many - maybe most - employers would rather see a dead employee than to risk a lawsuit. It is especially true in what I consider to be "high risk" jobs like convenience store clerks or pizza delivery folks. If I were ever forced to accept a job like that, I'd carry anyway. It's annoying enough to have to comply with government intrusion on my 2nd Amendment rights without surrendering to some boss or corporate dweeb.