It's common for airlines to sell seats on new international routes with the caveat pending government approval or awaiting regulatory clearance or some such language if the paperwork is not finalized. American Airlines will have the first word and the final one as to whether and when those flights will operate or not— if they cannot give you an answer, neither can we.
I checked the flight status for AA MIA-MID flights, and from the looks of things, they are still holding out hope that the approval will come through at any moment. AA4717 is still showing on the schedule for Thursday, November 17, 2016. But indeed, all flightrs since November 4 have been canceled.
Uncertainty over whether a flight will operate will probably not be accepted as an excuse to make flight changes without fees, but you can always attempt to call them and try.
Once the flight is canceled officially— which apparently occurs only a day or two in advance— what AA will do is governed by their Conditions of Carriage, the contract you agreed to when you purchased the ticket, and by their Customer Service Plan.
Since the airline does not have control over regulators' decisions, or their pace of approval, they could invoke the force majeure clause readily.
American may, in the event of a force majeure event, without notice, cancel, terminate, divert, postpone or delay any flight or the right of carriage or reservation of traffic accommodations without liability except to issue an involuntary refund. The involuntary refund will be made in the original form of payment in accordance with involuntary refund rules for any unused portion of the ticket. American will also reserve the right to determine if any departure or landing should be made without any liability except the afore mentioned involuntary refund.
(emphasis added) In other words, their only obligation to you, legally, is to return the money you paid. As you note, if this official cancellation occurs the day before your departure date, your money will not go as far in obtaining passage, but those are the breaks.
In practice, when there is a hurricane or baggage handler strike or something else which forces a cancellation, the airline will usually try to reaccommodate you. The options aren't necessarily good ones— once, with my EWR-ITH flight canceled due to weather, I was offered 1) a flight to BUF, three hours from ITH; 2) a flight to ITH three days later; 3) a partial refund. In the event, I took the refund and paid for a bus ticket. You'll need to consider what you'll be willing to accept.
In that light, American might offer any of the following:
- Rebook you on a MIA-DFW-MID flight (DFW-MID appears to be Saturday only)
- Rebook you on a MIA-CUN flight, as Cancun is the nearest airport to Merida they actively serve
- Reboook you on a MIA-MEX-MID flight (assuming their partnership with InterJet is still active, and InterJet is still operating MEX-MID), or MIA-DFW-MEX-MID, or some such
- (rarely) Rebook you on some other airline that serves that airport, e.g. United or AeroMexico
If none of those work, they should issue you a refund.