Well, without scripting, you could do this with a simple common event. First, make a variable, lets call it Enemies Dead. Now, go to your database, and to your troops, and make events to them, that check if the enemy is dead, and when it´s dead, it adds one to the variable (raises it by one). Then make a conditional branch that tracks the deaths. When it´s x, use the change party members command, and remove the mercinary. I´ll put a pic up soon.