Depending on how efficiently AA has dealt with the ATS Oasis Space bin mess (misrouted cabling, improper fastening of bins) they could have the 14 Oasis 738s they grounded back online. AA has 24 B38Ms in service (now grounded). And I suspect 738 pilots were cross trained on 7M8, and are certified to fly either - like 757 and 767 pilots are.
From the AA announcement:
On average, American operates 85 flights per day on the MAX 8, out of 6,700 departures throughout the American Airlines system. Our operations center is working to re-route aircraft throughout the system to cover as much of our schedule as we can.