Until March 31, 2015, if your checked-in bag on a domestic flight does not arrive within 20 min of your arrival, you can fill out this form within 3 days of flight to receive 2,500 miles. According to the website, “you must be a SkyMiles member at the time of travel to be eligible and requests for multiple flights must be submitted separately.”
Only one other airline that I know of does a guarantee and its Alaska Airlines. Their offer is $25 off a future flight or 2,500 miles if your baggage does not arrive within 20 min.
I wonder if this would be something that Delta will keep after the promotion. This might not help many but there will be someone who may benefit from this guarantee.