You have referred two entirely different issues, i.e., (1) resignation of director and the other (2) transfer of shares. So far as issue of shares is concerned, if he has actually subscribed as a part of paid up capital that are required to be issued as per the provisions of the company law. Non-issue of shares violates the provisions of the Company Act. Further, so far as the resignation is concerned, you will have to refer to the provisions made in the MOA & AOA of the company. Return of shares to the company has no relevance. Any one or even both the other directors should be ready to buy those shares as they may afford.