You didn't say where William Ray/Rey was in 1900, only that you found no record of him after 1900.I checked the 1900 U.S. Federal census, and I find the family as follows:
ENUMERATED 5 June 1900, Howell County, Missouri, Dry Creek Twp., line 88 on census:
WRAY, Wm. R., head, b. Oct 1845, age 54, married 30 years, b. Kentucky, farmer
WRAY, Sarah J., wife, b. Aug 1848, age 51, gave birth to 10 children, 7 survive, b. Kentucky
WRAY, William D., son, b. July 1887, born Missouri
WRAY, Clary (?) J., daughter, b. Feb 1888, age 12, born Missouri
WRAY, Finis, son, age 10, b. April 1890, b.Missouri
WRAY, Sadie E., daughter, age 7, b. Dec 1892, b. Missouri
Checking burials in Howell Co. on the assumption that William R. Ray/Wray/Rey died there, I find the following at www.findagrave.com:
William R. Ray, "At rest" born Oct 7, 1846 (very hard to read from the headstone photo); died 27, 1900
Note:someone took the headstone photo and transcribed his birth date as 1870; however, from the photo, the last number is clearly a 6 and not a 0.
To me, this appears to be your William R. Ray, but it would probably be helpful if you wrote to or contacted the Howell Co., Missouri, genealogy society and see if an obit appeared in the paper or whether they have a death record for him with more details.
I hope this helps you.