Not sure if the question is meant seriously. There is no shortage of countries in the developing world having all kinds of parental leave, and plenty of information how that is structured.
> bring in another person as a temp CFO for a year?
Yes, that's bascially how things are done. Either a temp hire or, more commonly for specialised roles perhaps, a consultant. There's a whole job market for doing these one year stints.
Of course, you can't force people into parental leave. Some doesn't take any at all. Some take as much as they can. It may very well be the case that specialists and business leaders take less time off than others, but it's not a general trend, especially not with the working class which is perhaps the opposite of what one might expect.
> Is the person entitled to their old job back?
Generally yes, but these things are hard to enforce.
> Do you fire the new person or the old one?
Not really since replacements are hired for a specific time period.
> if someone is definitely necessary in the near-day-to-day?
Then you have a problem but usually you know about it half a year before it's too late.
> things like passively selecting against women and younger people for critical roles. Is that how they manage?
There are plenty of data available on this. Comparing data from different countries is problematic, but countries with more social insurance tend to also have more women in leading positions. This is probably due to confounding effects of course but should be indicative that if the above effect exists it is comparably small.
> the women already did half the corporation's work for them.
I didn't quite understand this part.