It’s very rare that a situation would arise where a vendor wouldn’t show up on your wedding day.
You should read your contract and ask the vendors you meet with what their back-up plan is if they get sick or have a family emergency. A professional will have someone they can call to fill-in for them -- especially your photographer and videographer. The florist, baker and caterer have people working with them to create your wedding details so you may not even notice if the person you interviewed isn’t there on the day for set-up.
If a vendor can’t make it, he or she will most likely reach out to you as well as their back-up and notify you of the change in plans.
You should have a contact sheet with all your vendors’ names, email and numbers -- and list their back-up or secondary contact at the company too -- so you can contact them if you get concerned.
On the day of the wedding try to let it roll off your back and enjoy the day. When you’re back from your wedding you can call a lawyer, if necessary.