Does a marriage license ever expire?

No never. A license for marriage doesn't expire. You could get a divorce, but then you would be only separated in man's eyes not God's eyes. If you get married, plan to live with that man/woman your whole life because if you divorce that one and marry another, you are committing the sin of adultery in God's eyes.

Even in Jesus' day, there were divorces, and they were accepted by the church then. The Roman Catholic church requires a "tribunal" [like a court] to absolve you of your prior marriage so that you can re-marry another without being charged with adultery. The other Christian religions do not share this view ... in the Lutheran church, you can be married, divorced and re-married many times and you are NOT committing any sins nor adultery. In other words, you will not go straight to hell for getting re-married ... at the pearly gates on your day of reckoning, St. Peter will still allow your soul to enter heaven.

If you have gotten a marriage license issued, you generally have a year to use that license (getting married). After that time has elapsed, and you have not yet been married, you have to re-apply for another marriage license.