Driving style to make a high milage Prius last?

That's actually a good thing. The wear and tear on the traction battery seems to be minimal during highway driving.

The engine in the Prius seems to hold up to high mileage pretty well. We seem to get very few reports of failures here. Check the oil consumption as soon as you can and keep an eye on it. Of the few engine failures it's almost always people who never look at the dipstick and are none the wiser that there's a problem until the the oil light comes on. With that mileage I'd recommend sticking with 5W30 oil. Let us know if the engine is noticeably using any oil.

For longevity the main thing you want to do is put the least number of charge/discharge cycles on your HV (high voltage) battery. This means avoiding using the EV button if it has one (or dont install one if it doesn't) and avoid trying too hard to keep it in electric mode (which really doesn't improve fuel economy anyway).

At start up the car preferentially uses the electric motor instead of the engine while the engine is warming up. So the Prius is really super gentle on the engine in this respect. I don't know of any other car that babies the engine so nicely during cold starts. But to make the most of this you need to drive really easily for the first 40 to 60 seconds. So if you've got some quiet and flat local roads where you're starting from then it's ideal. But if you need to accelerate really hard (say to get up to speed on a major road) or if you need to go up a fairly steep hill while the engine is still cold then you're best off to leave it in park for 40 to 60 seconds and let it idle to warm up before driving. This is easier on both the electrics and the engine. (BTW. Leave it in park while warming up and it doesn't waste the excess power as it charges the HV battery while idling)

 

If you can't document that they've been changed in the last 20,000 miles or so, I would change the coolant and the CVT trans fluid.

Make sure and change both the engine coolant and the inverter/converter coolant, it's two separate cooling systems.

Use Toyota factory fluids. Super Long Life Coolant, and WS trans fluid.

 

This is the route that you should take. The hybrid battery is there primarily to capture energy from braking and release it for acceleration. While I think your battery has plenty of life left, given the prior instance of 80 miles one-way commute, the cells will have some wear and tear on them. There are ways that you can potentially stress the battery to the point of failure. For example, running down to 1 bar of SoC on the battery meter, and then hammering the throttle to get on the 70 mph expressway, could cause the weakest cell in the pack to reverse. But, even if your hybrid battery fails, there are repair options in the $500-$1500 range, so no big worries.

+1 on the transaxle fluid change.