If they draw against Mexico they just have to beat Poland by any margin and they are definitely through.
So in case Argentina win against Poland:
If Mexico wins last Match, Mexico would be first, Argentina second.
If Saudi Arabia wins last match, Saudia Arabia would be first (WTF!!) and Argentina second.
If Saudis and Mexico draw then it would be a three way between Saudis, Poland and Argentina on points where goal difference over all group matches comes as next criteria, so Saudis would be third and either Poland or Argentina first depending on margin of Argentia win.