There are some funny responses on here! 
As for the 'missing posters'... I suspect (but I could be wrong) that it's because a few of the old regular posters went to another site (the one that was trying to compete with mumsnet some 1.5 to 2 years ago,) and they made a huge song and a dance about how much better this other site was, and how mumsnet was just full of vipers, bitches, and witches.
This 'other' site seemed fab for 4 to 6 months, but went downhill very quickly, and got tedious and dull with sometimes only 4 or 5 people on the site some nights. So in late 2020, admin shut it down. It was open for about 10-11 months.
So the half a dozen or so old mumsnet users (who were quite well known on here but had become disillusioned with mumsnet for various reasons of their own,) couldn't really come back under their old name because they had berated mumsnet quite a lot.
I reckon they are definitely here under different names though. No-one ever leaves mumsnet. Bluntness100 is very likely under a new name too. One particular poster sounds a lot like her when she posts. (I won't say which one obvs!) So I suspect (like the others) that she has never left.