Funny part of all this is, that nowhere is written anything that you need return ticket. I even asked on Argentinian embassy, and they said no. When I appeared on airport, girl asked, where is my visa. Surprise, surprise, you can't board, if you can't present one... I showed "confirmation" mail (sent from friends email) on purchased ticket and they let me on the plane. She just printed boarding pass, and didn't write any data from my phone.
If in Argentina anyone would complicate, I would of course said, that it's first time I heard something like this. KLM, British and air France never asked for return ticket, only alitalia and iberia. Problem is, that they are carrying cost if you are rejected. You all know, what chance is for that here.
So I don't think, anyone can put you in jail, because you came in the country, that do not demand visa or return ticket. Also non of the airliners presented any info, except classic jibrish that you need papers in order.
8 years you probably get, if you kidnap a plane as well as present fake return ticket...