The remote chance of an unanticipated transaction like a UPS purchase of Atlas is one reason that there's a 180-day termination-for-convenience provision in the Amazon CMI contract. It would also be typical to have a provision that gives Amazon significant rights in the event of a change of control of Atlas. It would be customary for DHL and other significant CMI customers have similar provisions in their contracts.

Amazon has a lot of options, and a lot of leverage, in the unlikely event that such a transaction were to be proposed.

For what it's worth, I don't see how paying a premium over market value to buy a company that has significant value as an ongoing enterprise is a cost-efficient way of acquiring airframes (which is the rumoured reason for the transaction). It worked with Airtran because its stock price was floundering and Southwest not only got a pile of airframes in one shot but also the opportunity to eliminate a direct competitor and thus to raise prices. This isn't analogous, particularly because a large percentage of the AAWS airframes are on long-term dry leases to others or already owned by others and necessary for their own operations.