There tend to be LAN seats available to PUQ, so redeeming oneworld miles is almost certainly the way to go.

That said, if you buy domestic Chilean tickets in Chile (which includes setting that as your online location from abroad), such tickets are cheap, so it can sometimes make sense to buy your travel beyond SCL. PUQ is about as far as you can go, though, so it won't be dirt cheap, which is why you probably want to figure out how to redeem oneworld miles for the entire trip. It really shouldn't be that hard to do. From experience, I personally would consider this a relatively easy int'l award redemption.