Will grass fungus die out over winter, leaving the lawn fungus free in the spring or does something need to be applied now?
Grass fungus is probably more adapted to your climate than the grass is. Meaning that it will sit there all winter in a dormant state, then poke its little fungi head back up next year when conditions are right. In all probability you will need to treat the fungus to get rid of it, but in order to treat you need to know what fungus you are dealing with. You can get samples analyzed either at a garden store that deals with sod and lawn products, or at the county extension service. This link will help you locate the nearest office: https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm