I've never had this happen on AA, but on other airlines I've usually gotten a refund proportional to miles traveled; i.e. if ATL-DFW is 1/3 of the distance, they should refund 2/3.

It would seem to me you should get a refund of part of the miles too, and probably "refund" of the SWU.

You could probably get some additional compensation like miles, but they won't pay for your ticket DFW-SFO.

I assume you had a return ticket and used it? Sometimes if you don't actually go to your destination they'll refund the full ticket as a "trip in vain" - a trip that became pointless once you couldn't make a particular segment. For example, if you were traveling ATL-PHL-ATL for a meeting and never leave ATL because the flight is delayed/cancelled such that you can't make the meeting, they'll refund the entire ticket. But that doesn't seem to apply here.