One really really really important thing to get right is the fact that enzymes aren't alive in any sense, so they can't die. They're huge molecules made of many thousands of atoms which are the perfect structure to perform a very specific role.
Some cofactors contain chemical groups which are essential for the reaction to occur. Biotin is an important example in fatty acid synthesis.
Other cofactors have a more structural role. E.g. Magnesium is important in keeping ATP in a specific shape so that it can react. Zinc holds together regions of some DNA-binding proteins called zinc fingers. These fingers are held together in a specific arrangement by the zinc so that they can interact with DNA.