What happens if a non-immigrant requests an extension, but doesn't receive a reply before the requested extension date?

In the situation in which you describe having requested an extension and not receiving a decision before the date requested has passed, it is a good idea to file an additional I-539 asking for a further period of extension and documenting the reasons for the request. The question of whether someone can stay after the requested date has passed without doing anything further is murky, but the better practice is to request the further extension if you intend to stay. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.