Must I appear for failure to yield charge if the pedestrian walked away from the accident and refused treatment?

You still need to appear for whatever type of hearing is set.  Even when a "victim" does not want to go forward with charges, an officer can still make the decision to go forward.  If other people can testify about the same facts of the case without the victim, the State can also move forward and try to get a conviction. 

If you do not show up for court, regardless of the type of hearing, then the court can issue a capias for your arrest. 

As far as what to expect, you don't specifically mention what type of hearing that you are going to, but usually, the court's will have at least one preliminary hearing or "announcement" where they will inquire about basic procedural matters like:  do you have an attorney, how do you want to plea, do you want to talk to the prosecutor, if you do want an attorney-- then how long will you need.  The court will also give you a setting for your next court date.  The next date may either be another announcement to update the court on where you are at in disposing of your case.  Some courts however, will give you a trial date after your first announcement-- if just depends on your judge. 

If your notice says that it is set for trial, then you need to be prepared to defend the merits of your case.  This is where the officer an other witnesses will come give testimony against you.  You will also have the right to ask them questions and make an argument on your own behalf.  If you don't feel comfortable defending yourself, you should take steps to find a criminal defense attorney to represent you.