I fail to understand how you can actually have a `DH of 0 ft`, [...] You would be on the runway (hopefully!) at this point anyway. What now forms the basis of your `decision`. [...]?
I would say the DH is the (final) point at which you elect to continue the autoland, or go-around, and even with a DH of 0 ft there is still the rollout tracking and stopping part of the autoland left to go. If the aircraft landed way off to one side of the runway (or even the grass) instead of on the runway centreline, you might elect to go-around, even though you had "landed".