If you miss a court date, you might lose the case. This is called having a "default judgment" entered against you.
If you file a motion to undo ("vacate") the default judgment within 30 days, you will probably succeed. If it is has been more than 30 days, you must file a petition for "relief from the judgment."
This is very difficult, so you should talk to a lawyer about it if possible. The petition must be filed within 2 years of the judgment.
Updated: June 2018