After I got a site links for my site in google... If I change the site again the site links will be appear in google or not....
Every time you update a header, add a page or article or post or whatever. You may reskin it or even change the CMS. Whatever you have today, no matter how chuffed you are with it, you will want to change in the future.
Agree with your points, but I was wondering to know what kind of the changes, he is looking to make within the website so that one can suggest him whether the nature of changes would do negative effect over sitelinks or not.
As far as my knowledge, they will disappear. At the same time, the backlinks gained for old URL's will not be automatically transferred to the new ones, even if teh content is same. If the old links still appear in search results, you can request google to remove them if you wish.
If you are changing your site's URLs then the old URLs will show but not the old ones. For this purpse you need to add 301 re redirect code to the .htaccessfile placed at the root directory of the files.