If you are being fired, you generally do not "defend" yourself. Also, people at this level are very well-compensated, and the comp generally prices in the risk of things like this. Whether you are on leave or not scarcely matters unless you can show that you are fired because you are a parent (and that's an employment law issue).

It is my experience that people taking time off to be parents also take time off from the machinations that will lead getting promoted (at certain levels), thus hampering their advancement, but they are usually not fired, in tech anyway. Now the treatment of women, who already get a pretty bad deal even if they aren't mothers, is another matter altogether...