"Wrongful termination" is largely a myth. I know a lot of educated professionals who believe they have the right to a "fair" termination, but except for very specific instances, it isn't the case, and these threats go nowhere.

In most cases, unless there is a smoking gun, employers just sidestep the issue by targeting "layoffs", rather firing for cause.

The bigger issue HR deals with is sexual harassment or discrimination cases. And, even nuisance lawsuits can be expensive to deal with, and HR/clerical staff is a lot cheaper than lawyers.