It all depends on the characters. If they insist on killing each other
let them. This causes a larger problem for the person who did the killing
because now all those bandits who refused to attack the party because of
it's size no longer face this problem. The dead character can portray the
bandits. Over time the adventuring party will tire of killing each other
and bond. this has happened in several of my dming experiences. The
mutual enemy also works well. The spider or gorgon for instance. Hope
some of this helps.