I had a similar situation occur last week. Original routing was PHL-MSP-LAX-SMF. The PHL-MSP boarded... then deplaned due to MX.

I got rerouted on PHL-ATL-SMF with an overnight in ATL, arriving at SMF twelve hours later than scheduled on my original itinerary. (After some confusion when I walked into the SkyClub and was apparently the first to let those folks know that the PHL-MSP had not actually departed, but had instead deplaned. They couldn't help me at first because they system showed I was sitting on a plane that had departed. I believe they had to call the gate to get me taken off the plane in the system.)

I sat in the SkyClub for a while, and then recalled that I had checked a bag and asked the PHL SkyClub folks what would happen to it... they called baggage handling and made sure my bag was pulled off the plane (which was still sitting at the gate with no clear plan yet as to whether it was severely delayed or cancelled) and the bag was rerouted with me. (I did also have emergency clothes, etc., in my carry-one.) I don't know how well that would work in a big hub like ATL or DTW, but in PHL where Delta has a small presence, they managed to accommodate re-routing my bag with me. (And I was very pleased about that!)

Who knows what would have happened if I hadn't been proactive about it, but this time, all was well. My bag arrived in ATL with me, I picked it up, had it for the night, then rechecked it to SMF the next day.

Compensation-wise, they gave me 5000 miles a few days later (without me asking). That seemed a little weak compared to what others have reported getting, but other times they have given me way more compensation for far less hassle. There seems to be little rhyme or reason to their compensation decisions.