Who should attend the mediation seems like an easy question. Not so fast. There are a few things to consider.
Interestingly, a few weeks ago, I heard of a "party" being sanctioned for failing to follow the Court's Order that "someone with authority" attend a mediation on behalf of the insured. The insurance carrier for the "party" disagreed with the terms of the Order. All of this presents an interesting problem regarding the logistics of having all "relevant parties" present at the mediation.
It is critical to have an individual present at the mediation who can make a binding decision on behalf of the party. If the party is an individual, he or she must be present. If the party is a corporation, there must be an officer present who can bind the corporation. If an insurance company is involved, a representative with sufficient authority should be present. A dispute will likely not settle otherwise.