Could I be liable if I am aware my 93 year old father is a bad driver and gets into an accident?

Not based solely on the facts you've described, as you have no way of  preventing a licensed adult from driving.  He has no olbigation to listen to you, you have no right to take his keys or his car.  Theoretically you could start a court proceeding to have him declared incompetent and yourself appointed his guardian, or notify the police to be on the lookout for him as a dangerous driver, but you are not obligated to do so. Also theoretically you could try to get his insurance company to drop his coverage, which would make it illegal for him to drive, but again your are under no obligation to do so. There are circumstances where you culd be liable.  For example, if you were his legal guardian, or if he was driving on your behalf (i.e. to do an arrand you requested that he do), or if you entrusted him with your car, etc.