Generally they'll run it unless the conditions are truly apocalyptic.
https://scontent-lga3-1.xx.fbcdn.net...e5&oe=5B110C5F
That's my bike after a sleet race a few years ago. I was covered in ice too, was pretty metal. We sorta went from actively racing to understanding that we were all just trying to get to the finish. Make sure to dress right, it can be hard to balance staying warm enough with not overheating.