It wasn't too hard to figure out in the ArcGIS API for Python. Connect to the GIS and get your item by its ID.
gis = arcgis.GIS(profile_name=profile)
item = gis.content.get('abcdefghij1234567')
flc = FeatureLayerCollection.fromitem(item)
replicas = flc.replicas.get_list()
for r in replicas:
replica = flc.replicas.get(r['replicaID'])
create_date = datetime.datetime.fromtimestamp(replica['creationDate'] / 1000)
last_sync_date = 'n/a' # don't trust this to always be populated
if type(replica['lastSyncDate']) is int:
last_sync_date = datetime.datetime.fromtimestamp(replica['lastSyncDate'] / 1000)
print(f"{replica['replicaOwner']} created {replica['replicaName']} "
f"(ID {replica['replicaID']}) on {create_date}, last sync "
f"{last_sync_date}")
if replica['replicaName'] != 'MyReplica_abcdefgh12345':
continue
r1_flc.replicas.unregister(replica['replicaID'])
This code should work on layers with no replicas, since replicas will just be an empty list. In this case, I'm print out info for all replicas, looking for one with a specific ID, and deleting it. To overwrite the hosted feature layer, I will eventually want to delete all of them, but I want to coordinate that with my users first.
Note that this will break a Collector offline area connected to this replica. In my experiment, this layer is just a reference/background polygon layer, and I was entering new data into a different point layer. I collected a point in Collector, deleted the polygon layer's replica on the server, and was still able to sync my point back to AGOL. That said, I couldn't do anything else with the offline area after that (Collector won't open it), so I had to delete the offline area and re-create it.
