When a leader is known to be at front line of the battle, members of the opposition (or rebels) will deliberately cause problems that will escalate knowing fully well that he will be at the fore front.
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.