If they recruite 20,000 fighters; 10,000 will be assigned to face his army and other 10,000 fighters will be assigned to him alone to monitor every of his step and then terminate him.
It is a suicide mission for a president to be at the front line and a bonus for the rebels.
Everybody loves power. Immediate family members or close associate could easily plot agains a leader like Idris Deby because he is highly vulnerable.
Idris Deby first led a battle against bokoharam he succeeded. The last one was against the rebels who knew he will repeat what he did against bokoharam and plot for him.