Although I've done it many many times, it seems that a lot of things are changing, so I won't attempt to guess if it'll work tomorrow for me or for you. I have heard that many in the travel industry will often travel with one way tickets so it may not be as much of an outlier as you assume. I usually am asked at my originating US airport ticket counter, or gate, when I'll be returning to the US. As long as you provide a date within 90 days of departure, it's never been a problem. I don't recall ever having been questioned about it in Argentina.