PoSH COMPLAINT FILED AGAINST A PERSON WHO HAS LEFT THE COMPANY

Yes, a complaint can be filed against such a person even though he has left the company, and action can be brought against him as per the provisions of PoSH Act, section 9 of the act deals with the issue in question and is explained below:
PoSH Act 2013: Sexual Harassment of Women in the Workplace (Prevention, Prohibition and Remedy) Act 2013 says that:

Limitation period for filing complaint

According to the Act, a complaint must be filed "within three months from the date of the incident." Conversely, the ICC has the power to "extend the deadline" if "it is satisfied that circumstances prevented the women from filing the complaint within the given deadline."

Resolution of Dispute through conciliation

Prior to the commencement of an investigation and at the request of an aggrieved woman, the ICC may take steps to resolve the dispute between the aggrieved woman and the respondent through conciliation, provided that no monetary settlement is made as the basis of the conciliation.

Investigation procedure/timeline and powers of ICC

The ICC has two options: submit the victim's complaint to the police or open an investigation, which must be completed within 90 days. The ICC has powers similar to a civil court to subpoena and question people under oath, as well as to order discovery and production of documents.

Disclosure of the findings 

The ICC must report its findings to the employer within 10 days of the conclusion of the investigation. The report is to be made available to both parties.

Privacy clause

According to the act, the identity of the woman, the identity of the respondent and the witness, as well as any information regarding the questioning, recommendations and actions taken, are not disclosed.