The Texas Death Index Online lists William Wallace Marston died 9 July 1985 in Nacogdoches County, Texas. I am fairly sure this is the son because the SSDI also lists this death and shows the date of birth to be 2 April 1915. The SSN is 459-09-2344. You can probably get a line on some of his children (obituary?) and surely one of them will know what happened to grandpa!
The Texas Birth Index Online showed William Wallace Marston married to Inez WESTMORELAND and they had one daughter, Billie Jean Marston, b. 19 May 1937 in Wichita County, Texas. There may be more children born out of state or after 1949.
Suggest you try the GenWeb County Web Page for Nacogdoches County to see if someone will help you get William Wallace Marston's obituary. That Web Page may have someone listed that will do the obituary lookup but if not just put a message on the query forum askin for help. If you happen to be the daughter "Jean" mentioned above, you probably don't need the obituary because you will already have the information. If that is the case, contact me at email@example.com with any additional information you might have (last known location and approximate date, last comment from anyone regarding his possible location, any knowledge as to any remarriage, any reason to believe he stayed in Texas until his death?) and we will see if we can locate W.B. in some other way.