As long as you are in a decent location.
Rambo Einstein will just be among the last cannibals to die in a megacity.
When I think megacity I think “arm ants”. They can devour anything! It is easy to face the challenge of a few, but impossible when it is a few thousand.
I reject the mad-max scenario because human civilizations have failed so catastrophically in the past.
The worst it ever got was the princedoms that would become Germany during the 30 years war.
And people lived their lives even during that time.
All bets are off if it's a massive extinction event asteroid impact.
That would be tough. But a man-made non-nuclear event? We've been there, got T-shirts. The ones of us who's ancestors survived.
/johnny