Mileage and riding conditions will have a lot to do with spoke longevity. The rougher the roads the more the spokes flex and the sooner they will start to break. I too have ridden old bikes with a few broken spokes with no problem. If the bike doesn't have a lot of miles or hasn't been ridden regularly over very rough terrain then I wouldn't ride it and re-lace the wheels with fresh spokes. Never heard of cold hot cycles causing breakage. You can just replace a single spoke but chances are you will just soon find another broken.

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