They won't survive boiling water, or being baked in the oven. I always do that to coco, no matter what, for a good piece of mind. Whether its been sitting around or new, but mostly if i'm using indoors. I use boiling water to expand my blocks, and let it pasteurize as it cools off. No chance of any kinds of dormant pests or eggs surviving that..
I've literally watch gnats fly from one stack of organic soil bags into all the other different stacks next to, it at my buddies grow shop he worked at. It's impossible to keep pests away when multiple loads of products are coming in on pallets from different trucks, from different facilities all over the country. I imagine its the same wherever you buy your stuff. They keep all the grow mediums in one big room somewhere.
I don't use coco that often anymore so its not too big of a chore when I do. If I need a little bit that's already to go, and been sitting around awhile, I might even toss it on a tray and bake in the oven, for a few smaller pots worth anyway.
I wouldn't worry as much if its staying outside. Sounds like you'll just get mites anyway.. They are overwintering everywhere outside and around your patio from the sounds of it.
