What happens if a satellite slows down so much that it falls out of its orbit?

If a satellite slows down significantly and falls out of its orbit, it will begin to descend toward Earth due to gravity. As it approaches the atmosphere, it will encounter increasing friction, which can cause it to heat up and potentially burn up upon re-entry. If it survives this process, it may crash to the Earth's surface, possibly in an uninhabited area, or create debris if it breaks apart. In either case, the satellite would cease to function and be considered lost.