[Ombudsman]

If there is a significant schedule change, in this case Delta no longer flies ATL to PVR non-stop, the airline should honor your existing reservation and book you on the most direct routing possible without an overnight stay even if it means booking you on flights which currently have no award availability. You are most likely being forced to accept the routing through MSP as it is all Delta operated flights and those flights most likely had award availability. The reason they are reluctant to rebook you on the same-day itinerary via Mexico City is the MEX to PVR segment is operated by AeroMexico and Delta will have to pay AM to fly you to/from PVR.

If DL refuses to re-book you on the same-day itinerary then file a complaint with the DOT. When DL "merged" with Northwest it left only one SkyTeam carrier in North America. Bad decision by the DOT and DOJ if you ask me as it leaves few options for rebooking on "partner" airlines when no partner airline exists.