It seems that not everybody remembers the world in 1967.
To begin with, there was no such thing as no-fault divorce. A divorce had to involve one "guilty" party, and one "innocent" party. Two "guilty" parties would just be blown off with "You two deserve each other." And it was regarded as standard good manners for the man to offer himself up as "guilty", unless the woman was a complete slut or psycho. (See "The Gay Divorcée" for an example of a man who /doesn't/ follow this social rule, because he's a pig.)
Now, also during this period, the usual rule was that the wife got the kids, and the wife and kids were entitled to be just as well off as they had been before the divorce. (Remember, as far as the Law was concerned, she and they were officially innocent victims of the Big Bad Man.) So alimony could be very high indeed.
As to her getting a job....
There was no such thing as professional daycare. If a divorced woman were poor, she could probably leave the kids with a neighbor, because poor folks have been doing that for thousands of years, but for a middle-class divorced woman to do that would have been regarded as shameless freeloading.
There were relatively few jobs for women, and even fewer that paid decently. A woman could be a secretary, but shorthand and typing take years of practice. (There were no personal computers then; few people could type except for writers and secretaries.) And secretaries didn't make much more than minimum wage, anyway. The same for stitchers in clothing factories (America had clothing factories back then). Beautician? Cleaning woman? Hotel maid? Nurse? None of them paid all that well. There were a handful of woman doctors, lawyers, and the like, but the closest pointer to the future was that there have always been quite a few women in computer programming. But you couldn't just walk in and ask for a programming job if you'd never done it before.
In short, this movie makes the usual exaggerations you expect in a comedy, but it is nowhere near "preposterous" or "ridiculously unrealistic". It's pretty solidly grounded in 1967 reality.
Now, on the other hand, I can't say I like the movie all that much. I guess I'm too romantic to take divorce as a joke. But the performances are sound, and I have to say that Van Dyke and Reynolds both had guts to tackle this script at all. Both of them have always been typecast as "lovable".
