I don't think I'd cancel your trip based on what El Nino affect may or may not have on weather in Chile. With climate change it's now harder than ever to predict weather patterns. Now it's all about extremes. But it's unlikely the weather in Coastal Chile would be the same in Inland Chile, or high mountain Chile.

Now we see record breaking EVERYTHING, all over the world.
Record Cold, Record HOT, Most rain, Most snow, most severe floods, severe drought. It's all out there happening NOW, worldwide. It's Global Warming. It's real.

Seems predictable seasonal patterns don't always follow protocol now.

El Nino, IMHO, is connected to this, but exactly how?? Your best move is to be mobile and willing to move quickly, go with the flow. Go to where the weather suits you. Stay away from areas of extremes when possible. Or be happy to sit and wait for things to clear so you can safely pass. Keeping up with current reports where you are (and where you want to go) is key.

None of this should be a surprise to anyone in the field or anyone following weather patterns for a while. I first saw it coming ... CLEARLY ... in the late 1970's while working in Antarctica.

Scientists there studying glacier movement and documenting the break off of huge tabular Ice bergs off major Ice shelves had early clues on this. Even then, the numbers were staggering and it was obvious something was up.

No one called it Global Warming then ... but they understood that it wouldn't just be a case of higher world wide temps ... the experts knew that ALL weather ... worldwide ... would be affected. So ... HOTTER,
Colder, Wetter, Dryer, Windier ... take your pick! The so called "tipping point" is long past.

Enjoy the ride!