Source: Apple
If you want to get your iPhone XS (or newer iPhone) repaired because of a Face ID issue in the future, it might not mean your device will get entirely replaced. The company will reportedly give Apple Stores and Apple Authorized Service Providers access to a new TrueDepth Camera service part that includes the Face ID and front-camera modules. This will allow them to perform same-unit repairs on your smartphone with Face ID troubles.
As described in an internal memo provided to MacRumors, the move is meant to reduce the carbon footprint of Apple's products by lessening the number of whole-unit repairs. It also means you don't have to set up a new iPhone because of some Face ID trouble, or it could cost less, but the memo didn't mention pricing. It isn't known when this repair process will be offered, but Apple told its technicians they will receive training and documentation at a later date.