A similar rule applies for the ATPL exams. In the past the CAA has agreed to restart the sequence part-way-through if they considered the circumstances warranted it. If for example a student signed up for a distance learning course but then found that he/she could not learn that way, the student might decide to transfer to a full-time course. Or a student might find that his/her school was rubbish and decide to go to a different school. If a significant part of the time/attempts/sittings limits have already been used up, it makes sense to start afresh. I have known the CAA agree to this for the ATPL exams on quite a few occasions.
Although the PPL situation is slightly different, I suspect that a similar level of flexibility would be applied. Spending 16 months in a coma following a car crash after passing the first exam, would probably get you a restart. But bone idleness would not.