Phil,
Indeed. It is often called 'chopped'. However on my initial course one of the cadet's whose father was a tug-boat skipper died. This meant that his brother needed help to keep the family business going.
The cadet was a first rate chap and he was not allowed to leave until he had finished his initial training. Once he was ready to graduate there was then an opportunity to decline a commission and leave, which is what he did.
I suspect that the staff simply wanted him to continue to the end.
The other way is voluntary withdrawing from training.