The ArcPy Data Access Insert Cursor returns the OID after inserting a new record:
with arcpy.da.SearchCursor(finalFC, fieldnames, 'OBJECTID = {}'.format(oid)) as fscur:
for fsrow in fscur:
with arcpy.da.InsertCursor(scratchFC, fieldnames) as icur:
ioid = icur.insertRow(fsrow)
print(ioid)
del icur