Flyingfish123:
I am sorry to hear about this. Hopefully you get into a great program so you won't have to worry about finding a new job! Responding to your two questions:
Q: Should I update the schools before or after the release of decisions, or not mention until they ask?
A: You should just hold your cards. Do not mention anything. You are under no obligation to update the school about your profile post-submission, much less post-interview.
Q: if I’m to update the schools, what’s the best way to address it?
A: You can send an email or call the admissions committee and indicate that you were laid off as part of a massive restructuring on X date, just as you did in your posting. So long as that is true, your (hopeful) acceptance will not be rescinded because you were accurate on your application. I assume you have proof of your dismissal in the form of a termination letter, so if there is an issue you can always submit that to show you were employed up until X date.
Again, I am sorry you have to go through this but fortunately I am confident this will have zero impact on the MBA admissions process for you.
Good luck and hoping for the best,
Admissionado