I also wanted to confirm that cancellation fees are limited to $5.60 paid in taxes. I asked to cancellation a Delta flight due to recent disruption. They said they did not offer free cancellation (I believe DOT requires Delta to do so). But I can get miles back while they keep the taxes already collected.

Does it sound like it is their policy to refund miles and you pay the less of $50 or collected taxes as cancellation fee?

This would be very advantageous when booking Delta domestic flights speculatively. They are much cheaper, but there is no availability within 3 weeks.