Santer sure was in the second Winnetou novel; I think he died at the end of the third
Apparently the survival of Santer was too much for Rialto films so they killed him in the first film
When Karl May published his books, people were more used to continuing stories, with villains and storylines that were transported from one novel to another; remember Old Surehand : it takes us several books to find out what exactly is his secret
Most classic novels of writers like Dickens or Balzac were published in weekly, or monthly, installments
Today we know, of course, the Star Wars and Lord of the Rings sagas, but in the early sixties it wouldn't have been a good surprise to most people to see a villain like Santer survive a movie.