I've had them try to cancel my holiday, and I've been called and had to give guidence over the phone while on holiday, but they've never (successfully) dragged me back.

They tried to cancel my NZ trip earlier this year, but when I pointed out they would have to rebook my flights and hotels with cash instead of points and miles due to availability, they weren't too happy about stomaching 20 grand, so they thought better of it!!