This is one of the interesting situations that I faced few months back. I had an SEO client whose website had a good presence on the web with decent and quality traffic. The site had a Google Page rank of 6 and was pretty popular in its industry. The site was also blessed with Google Site Links, which is the mark of the search engine popularity for the site. The client had just started their SEO contract and they had the site links for the last one year.
Just before entering into the SEO contract with us they made changes in all the URL names via their previous vendor and also deleted the old URLs. When they started with us we were happy to see the Google site links. But suddenly after a week the site links disappeared and the client started complaining over that. I was really shocked and really was not able to find the reason. After a thorough research I came to know about the URL changes that the previous vendor has made. Actually the URLs which appeared in the Google Site Links also changed and as a result the site links got disappeared. I knew that we can never create Google site links, but only manage them via Google Webmasters Tool.
I told the client about this and consoled them that we would try our best to bring them back. Fortunately the site maintained its ranking and traffic and after a few months the site again got its Site Links. The client was happy again and continued smoothly with us. There were certain things that I learned from this, and I always followed them going forward. They are listed below.
1) While changing the URLs of a website having Site Link, implement 301 redirect for the old URLs.
2) Don’t delete the old URLs at least for a few months, so that everything becomes stable.
3) It is better not to make any changes on the links appearing as Site Links.
4) Before changing the URL name, first consult with the SEO or webmaster.
Hope this would be applicable to all of you and take care in taking precaution before changing your URL names.