Have you looked at the burial register of the church where they were married (by tracing the congregation of the minister on the marriage record). Many Milwaukee area Protestant church records are available in library collections.
I don't find a clear match in "Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950).
For more specific information contact:
Gary Rebholz, compiler/editor
Indexing Milwaukee's German newspapers continuously since 2007... helping to access our historic German-American culture.