If I get subpoena as a witness in a civil claim, I'm I legally obligated to appear?

Last year, a temporary employee got fired while he was injured on an L & I claim. He was fired for being "insubordinate" I gave a witness statement via writing. A year later, I received a call from the State Attorney General office about being mailed a notice to attend court. I'm not thrilled. Do I have to attend if I quit my job before the date? Thanks for any insight!