Sarah Landau is on the 1905 NJ State Census with three children - Annie, Manuel & Florence.
Morris Landau is not there, so he must have passed on prior to June 1905.
The last year that Morris Landau appears in Paterson city directories is 1905. In 1906 Sarah Landau is listed as the widow of Morris.
You can assume that Morris Landau passed on sometime in 1904 or the first half of 1905 probably. They had to collect the directory information some time prior to publishing.
This is the family on the 1900 census with the surname misspelled.
You can request the death certificate:
If you search Landau at this site
you will see that Morris Landau naturalized in Passaic County in 1903. You can see his nat papers at the above free site. Morris gives his birthplace as Glotz, Russia.
Also, have you seen The Morning Call (Paterson) newspaper description of Annie Landau's 1908 wedding? If not, let me know and I can email it to you.
Good luck in your search,
RATOWSKY / CHAIMSON (Ariogala, Lith.); LEFFENFELD / FINK / KALTER (Daliowa & Jasliska, Pol.)
BOJDA / BLEIWEISS (Tarnow & Tarnobrzeg, Pol.); WALTZMAN / WALZMAN (Ustrzyki Dolne, Pol.)
LEVY (Tyrawa Woloska, Pol.); SOLON / SOLAN / SOKOLSKY (Grodek, Bialystok, Pol.)
BOBISH / BLUMENKRANZ / APPEL / WEINER / ROSENBERG (Vysoko-Litovsk, Brest, Biala Podlaska)