Smith decided to put up the racket for good after a year marked by injury and boredom. Before the loss to Vopickova she only lost to King (twice), Richey and Krantzcke during the year so she was still playing well.
If she had retired and not come back late the next year, her statistics prior to retirement would have been 7 (straight) Australians, 2 French, 2 Wimbledon’s and 2 US Championships for a total of 13 Grand Slams. From the matches found so far (small amount missing) her singles win-loss record would have been 554-46 (92.3%) with at least 99 (+1 shared) singles tournament wins.
Only one can speculate how she would have been viewed in tennis history if she had stopped playing in 1966.