Don't do anything like going to ICAI, talking to his wife, or anyone else. Just go straight to the cops and file a complaint. Show all the messages and it should be proved that they emanated from the principal's phone number.... He will be liable for imprisonment upto 3 years and fine upto 5 lakhs under the Information Technology Act as ammended 2008.
Don't worry about anything else. ICAI will automatially take care of your transfer to another Principal.
You have to make an example to the Student Community. Don't spare such perverts.