@ackk
So far what we found is that OINP officers couldn't care less for what you do about your job after your nomination.
Your situation is quite the same as my wife. She applied to PR and then changed her job for reasons beyond her control. She informed OINP by email about her job change, so they can't say she is omitting the information. Nobody from OINP bothered replying her email so far. This is actually all you can do, and I´m sure there will be hundreds of applicants in the same situation in this "International Student - Employer job offer" stream, since nobody can guarantee that your first full-time job in Canada will last for at least 2 years until PR is approved.
There are 2 possible scenarios, considering OINP is so far ignoring job changes after nomination:
1 - IRCC won´t check again on your job, since OINP has done it already. This is probably what will happen to most of the cases.
2 - You are unlucky, and the IRCC officer decides to check again on your job. Then they will come to you, and you will explain to them that all these changes happened after your PNP approval and PR application. You show the email that you sent OINP to update your job situation, and hope for the best.
Contact OINP by phone and explain your situation. If you get any new information about actions to be taken please keep us posted.
I would say OINP would only drop your nomination if they realize you lied about something, or you no longer intend to settle in Ontario.