There is no automatic rule that status continues unchanged through an unpaid leave. TN rests on prearranged professional employment with the employer, so whether the requirements are still met depends on the nature of the leave and the state of the employment relationship. That assessment has to be individual.
Describe the arrangement precisely to counsel
Counsel needs the facts, not the label: who initiated the leave, what the employer says about the employment continuing, whether any work is being performed, and what the expected return looks like. Small differences change the analysis. Provide the leave letter, the original support letter describing the professional duties, and the admission or approval records, so the advice rests on documents rather than descriptions.
Bring the documents in a fixed order so nothing is described from memory: the support letter that set out the professional duties, the admission record, any approval notice, then the leave notice itself. Counsel reads them against each other, because the question is whether what was represented at admission still describes the arrangement. Two facts do most of the work — whether the employer regards the employment as continuing, and whether any professional duties are still being performed — and both should come from a document rather than a conversation.
Hypothetical example: a land surveyor keeps an email thread confirming that project work stopped on a stated date, which fixes the timeline that a later account from memory would blur.