Does PHP scripts always finish, or are they halted if the web page loading is halted?

I've made some scripts that let a user work on a MySQL database via the web. When a web user clicks a button in an HTML form, a new page is loaded which runs PHP scripts which in turn manipulate the database accourding to the users's request. However I'm worried that the scripts may halt if the web user halts the loading of the web page which is running the scripts, leaving the database "corrupt" due to incomplete manipulation. I'm also worried the same could happen if the web page is not successfully loaded due to network problems. So to the real question: Does PHP always finish off the execution of scripts, or does that depend on whether the web page is indeed successfully loaded?