Thanks for chiming in. I agree. Sync replicas would be a fine way to do this work if that was supported well in Runtime. Unfortunately, it looks like the symbology that is published with UN feature services is not published to Server, only to Portal. So, the sync replicas don't contain any of the rich CIM-JSON symbology used when looking at an online layer. So, when we tested this fully offline, the map is really stark with just plain gray lines and points.
As for UN tracing, this might be odd. Each Geodatabase object in Runtime is a representative of one sync replica. The Geodatabase object is how you get the UtilityNetwork:
https://developers.arcgis.com/net/api-reference/api/netwin/Esri.ArcGISRuntime/Esri.ArcGISRuntime.Dat...
If you had separate replicas covering different areas of the map, each would have their own UtilityNetworks. I don't think one can specify multiple UtilityNetworks for a trace. So, any one trace would be confined to a single area. I guess one could dig around in a trace result, looking for edges that spanned into other areas and then continue the trace into those regions too. But, not very easy to manage. Certainly feels like something Runtime should manage.