As others have said, call. You will likely be taken care of (including an earlier flight provided it has availability).
OP: By "availability" here, we mean that delta is willing to sell a coach seat, at any price.
Basically, you should be able to look on DL.com, and if you can buy a coach ticket on an itinerary from BHM->LAS within a day or so of your original flight (even if DL wants $2000 for it), you should be able to call and get yourself on those flights. You don't need to see it for the same price.
As others wrote, the same may also hold true for ATL->LAS.
If you have two separate tickets BHM->LAS and then LAS->BHM, (or even if not), these changes really shouldn't affect your return trip.