You'd think it was more than that given the media outcry at the time. 8,000 out of ~6.8 billion is a complete nothing... more people probably died in car accidents in the same time period.
[1]: http://wiki.answers.com/Q/How_many_deaths_are_caused_by_car_...
[1] 20-50 mil 1918 flu pandemic http://en.m.wikipedia.org/wiki/1918_flu_pandemic
If over 7k people had confirmed SARS and survived, many more probably had mild cases that were never disambiguated from other seasonal respiratory illnesses. Perhaps they 'superspread' milder viral variants which spoiled the 'herd' for nastier variants.
It's certainly possible that some people got "low-grade" or even asymptomatic SARS. However, given how it spread like wildfire through exposed populations (such as health-care workers) it does seem that many people were susceptible to the virus and developed severe symptoms when exposed.
Therefore it seems unlikely that antibodies built up in the "herd" had much to do with the pandemic ending. The credit goes to the massive public health response, especially isolating anybody with suspected contact. SARS had all the components needed for a bad pandemic; they probably saved tens of millions of lives.