Usually, yes. There are some reasons why it might not.

1. We take your site to the first page of google, by overseeing changes that convince Google it is one of the best sites around, and worthy of being in google's top 10. The problem is, other web site owners may decide to put in a big effort and improve their sites down the track after our work has been completed. They may add lots of new and useful content, fix their own search engine penalty problems…If enough of your competitors do this the result may be that Google values these improved sites above yours and your rankings will fall. In such cases, we can usually fix the problem for you for a small top up fee.
2. Your web developer might do something that breaks what we have done. Your site may have been broken for a while, some of our work might have been removed etc. In such circumstances, we can usually fix the problem quickly, or advise your web developer what to do to fix it.

NEW: due to great demand we are now offering maintenance plans, where we monitor your site and alert you when any problems (like the two described above) occur, or just before they become a problem.