If landing in Beunos Aries could I drive south to the tip back up through Chile over to Bolivia and back to BA in this time. Do some day trekking and mix in a 4-5 day W trek? Thanks

Theoretically, you could in that sort of timespan but, in my experience, few, if any rental companies, will allow cross border rentals. The exception could be Argentina/Chile but even there, the paperwork required and the cost could be prohibitive.

Even with seven weeks, the distances are vast, the roads rough, sometimes very rough. 70% of roads in Argentina are un-paved, in Bolivia, perhaps more. Some parts of that route are stunning in terms of scenery are stunning, others, like the pampas can get very tedious after a few hours.