Wil slices and dices the issue better than anyone.
Apple handles a sales slowdown the old fashioned way. On the surface, in public, you’ll see what we see already; discounts, promotions, bundles and packages, trade-ins, etc. Below the surface and out of sight, we’ll see Apple make deals with big retailers (think Best Buy, Target, et al) and cellphone carriers (AT&T, Verizon, T-Mobile, et al) so they can create attractively priced bundles like free devices or BOGO (buy one, get one for x-amount off or free).
That’s how it works, folks.