I know of one person who, on not meeting his offer at Jesus, was offered a place at Homerton. Another person missed his offer from Homerton, and was accepted by them anyway. Make from this what you will.
Also, didn't Vanessa (Pikasomething on these boards) get fished by Queen's from Downing after she narrowly missed her IB offer? I might be remembering that wrongly.
So whilst it's not something you should rely on or expect, it -does- happen. And, in my experience, not all that uncommonly (but obviously I'd be more likely to know people who did get fished/taken anyway than people who didn't).