How do flies survive the winter?

There are three potential answers to your Q.

Many flies try to hide where its warm, underground or in trees and go in a "coma" where their heartbeat slows and they are in a near-hibernation stage.

A more general answer is that the fly lays its eggs somewhere warm (mentioned above), then the fly dies. The larvae then hatch when its warm thus creating new flies. I heard the the typical "nat" lives no more than 24 hours, concluding it's impossible for most flies to survive an entire winter.

Lastly some flies such as mantises and dragonflies lay their eggs underwater to protect them from the freeze.