The Summons Expires
Technically, your divorce petition or complaint doesn't expire if you don't serve it on your spouse -- but the corresponding summons does. A summons is an additional document you must file with your petition in most states, informing your spouse that you're suing him for divorce. The amount of time you have to serve your summons, along with the petition, can be as short as four months in New York, or up to two years in California. Sometimes county rules can override state rules, so check with your local courthouse to be sure how much time you have.
The Court Can Dismiss
If your summons expires for lack of service, some states will dismiss your divorce pleadings. In other jurisdictions, dismissal may not be automatic. However, if your summons isn't valid anymore, you can't serve it with your petition, and without service, the divorce will not move forward. This doesn't mean you have to stay married though. You can refile for divorce and start over. If you couldn't serve your spouse because you don't know where he is, it's possible that you may be able to achieve service through other methods, such as posting a notice in a newspaper.