Hi Keith,
If you are planning to use the Survey123 field app without wifi or cell phone network connection (offline mode), you need to ensure you have an offline map package (.tpk, .vtpk, .mmpk) loaded on the device before you go offline. However, if you are in the field and have access to cell phone (4G/3G) coverage or satellite internet coverage, then online basemaps will continue to work.
The geopoint, geoshape and geotrace question types (map questions) require a basemap to be able to capture the point/line/polygon in the detailed map view, so that there is a visual and spatial reference to the shape you are collecting. When you are offline, the default online hosted basemaps can not be loaded, so you need to ensure you have an offline map package of the basemap you want loaded to the device, so it can be displayed for the area of interest.
You can find out more information about creating offline map packages for Survey123 here: Prepare basemaps for offline use—Survey123 for ArcGIS | Documentation
Regards,
Phil.