Does a Form 27 saying "not worked" expose the patent to a compulsory licence?

It is a relevant input, not a trigger. Under Section 84, any interested person may apply for a compulsory licence at any time after three years from grant, on grounds that include the patented invention not being worked in the territory of India. Form 27 filings form part of the public record an applicant would rely on.

The practical answer is not to leave the form blank or to file it carelessly, but to state the position accurately and to record the steps being taken towards working — including licensing availability, importation, and regulatory or market-entry constraints where these explain the position.