It is pretty easy to visit BA and various spots in Uruguay like Montevideo, Colonia, and Punta del Este by flying in to BA and traveling by ferry/bus. I'd recommend a trip to Iguazu Falls at some point on your journey, perhaps transiting from Brazil to Argentina that way.

Patagonia in Southern Argentina has some great places to visit, including Calafate and perhaps Ushuaia, though these are a long trip, perhaps best made by air.

I loved Bariloche and the mountain areas, which are doable by land transit from BA. I don't know if you could still go skiing there that late - the Argentinos can weigh in on that. Mendoza is a great place to spend some time enjoying wine tasting and trips up into the Andes; again, a trip, but doable by land from BA.

Argentina is a very large country with huge numbers of things to see and do.

Have fun! I wish I had that kind of time off....