What happens if I use a ripped contact lens?

You risk infection. Torn contacts have sharp edges that can scratch the eye. This can in turn allow bacteria from the contact or eye surface to get under the skin and cause a serious eye infection. Do not use a torn contact lens!
Ouch. A damaged lens can cause irritation to the cornea and conjunctiva and may cause a corneal abrasion. Best not to wear and replace asap.