Originally Posted by
RatherBeOnATrain
MARTA runs less frequently and often does trackwork on Sundays, so you may want to use Uber or a Taxi.... especially for your return trip since the train doesn't have a station at the international terminal.
As far as I know, the only airline flying ATL-SDQ is Delta, so he would be fine to return to the domestic terminal even if he picks up some new luggage while out in the city that he decides to check.