Value of a case depends on many factors such as lost wages, lost benefits, whether you sought psychological treatment, etc. It would be impossible to answer that with this amount of information.
It does depend on many factors and requires much information and thought, as well as consideration of the circumstances. Moreover, it will depend on the defendant and it's view of liability and litigation, as well as you and what you are willing to settle for. Litigation is about problem solving, and mediation is one way to attempt to do that, looking at both the risk of going to trial for both sides, and the potential value of the case should that occur.
There are tangibles to consider: Your past wage loss, your future wage loss (depending on your age), and intangibles: emotional impact to you, you as a witness and a person, defendant's witnesses, whether defendants are lying. Your attorney should be able to assess the value of the case and give you an idea of the range of settlement potential in mediation, as will the mediator once presented with all the facts (presumably)