Smart! We cannot know whether the mass is conserved or not without actually doing the experiment! Thankfully for us, scientists conducted the experiments a long time ago and found that mass is conserved in all such chemical reactions.
This is called the Law of Conservation of Mass. It states that mass can neither be created nor destroyed in a chemical reaction. The burning of the matchstick was just one example of a chemical reaction. But, scientists discovered that the Law holds for all chemical reactions.