I think that since the South Rim Dr is maintained by the NPS it should remain, since it does in fact connect to US 191 at its west end.
Well, see but what's maintained by NPS is
this, which... isn't actually part of South Rim Drive, it's "Spider Rock Overlook Access Road". South Rim Drive proper is entirely maintained by BIA. The NPS-maintained roadway doesn't connect to US 191.
Anyway it's been over a week and no further commentary has been received, so proceeding with deletion.