Google is fickle. Your number 1 site today - can always get trashed in a Google update tomorrow.
I always have a back-up site. Same topic, different keyword, different content. And I promote the back-up site differently than I do the main site. That way, if the big G decides for some reason that my site shouldn't be in the top 50, I always have a site either ranking on the second page that I can start pushing or a site ranking on the first page for a different keyword.
This gives me time to figure out what happened to my main site - without a big loss of revenue.
What is YOUR back-up plan if Google decides to drop your site from #1 to #100?