Here's our deal:
I'm going from Buenos Aires (EZE) to Panama City (PTY) for vacations. 2 adults, 1 child.
Copa Airlines' rate from EZE to PANAMA (non-stop) is US$ 3900 for the three of us.

Now, if I book a Buenos Aires to Quito, same airline, with a change of flights in Panama, the price drops to US$ 2144.

Obviously, we want to book the Quito flight, get off in Panama and STAY THERE. We don't want to travel from Panama to Quito, nor from Quito to Panama.
We will not check any luggage.

My concern is for the return trip, we would skip the QUITO - PTY segment. We would just take the plane at PTY and go home to Buenos Aires.

I tried booking all segments separately but the fare increases. It's unbelievable, but it's the way it is.

So, is this doable? What are the risks or the costs, if any?
Please let me know what you think. It's a really huge difference in fares, we'd be saving ourselves almost US$ 1800.

Any tips will be appreciated. Thank you all so much.