skipping the last leg of the flight
I know in the old days ( back in the 90's) one could skip the last leg of a flight and it wasn't a big deal (the old "hidden city" routing I believe they called it).
Now you can't do that because of security.
If someone travels without any checked baggage and just get's off before taking the last leg of a flight (say JFK-ORD-LAX and on the return goes LAX-ORD and get's off in ORD without finishing the entire trip back to the origin) would the airline invalidate the miles for the entire trip?
Thanks