Question about hair and makeup artists...

Do they have back-ups in case they get sick the day of the wedding? I was kind of thinking that they probably don't or that if something happened they may try to refer you to someone. Does anyone know? My mom was asking me this today and I said if a makeup artist flakes I could do my own makeup since I do it everyday (I would prefer not to) and for hair I guess you can run to a salon. Does anyone know if they do actually have backups? I hope my post doesn't scare anyone