For a more complicated situation like that, it would need to be decided by a court.
But with what I wrote about concerning negative statements of fact that are proven to be untrue, the courts will most likely deem them to be defamatory. Even if they were meant for a "positive" outcome, the statements on face value can be argued as causing more harm than good. If 10 years from now someone comes across the negative post, how is he/she suppose to know the context they were given in? He/she will take them at face value as a negative aspect about the company.
IMO
Best to all.