Australian travelling from Argentina to Chile

If the road was likely to be snowed in, I doubt the bus co. would be scheduling a trip.

You value your time at only 10 AUD per hour?

Ah I remember the good old says of travelling by bus trough South America, back when I had more time than money.
At one point we contemplated travelling by bus from Quito to Sao Paolo, via Lima and trough the Amazon in order to save money on a flight. The trip would have taken a week. I was gearing up for a bit of an adventure, when we luckily found a flight that was only a bit more expensive than the bus. In the end I am glad I spent that week on a beach in Brazil rather than on a bus.
My point with this is that you should really consider how much money your time is worth. If you do have more time than money, perhaps consider stopping along the way to break up the journey in say, Mendoza.

Consider going by the Lakes Crossing via boats and shuttle buses. We flew BsAs to Bariloche, did the crossing spending a night in Puella ( most passengers kept going) and then arrived in Puerto Varas, Chile. Flew to Santiago from Puerto Montt. We spent time in both Bariloche and Puerto Varies, beautiful places.When crossing the border between Argentina and Chile you will be in a national park. Hold on to the piece of paper you are given when crossing. Our luggage was gone through at the border as was everyone else"s.

I agree with Suki.

Bariloche is a small city in a mountainous area [the andes] on the edge of a huge lake. Beautiful. Reminded me of Switzerland. Delicious chocolate. If you have time, take the train from BA to Bariloche. If not, then try to spend multiple days crossing to the Pacific Ocean. Mountains and lakes and forests.
Consider local ferry from Puerto Montt to Santiago port.
Harvey