Before you take out the enemy general you need to pull the warmasters and other NPCs who guard the general. It's a good idea to assign a main tank to the job of tanking these hard-hitting NPCs, with plenty of healing to back them up. If everyone does their role, the process will go much more smoothly. If a player rushes in and engages the general before the guards have been killed, they should just die in place rather than running out, as that will draw the general out as well.