Plot hole: Both Vesper and James are needed alive if Le Chiffre is to steal the money. But the trap on the road could have easily killed at least one of them (Bond isn't looking too good afterwards), or even both.
Plot hole: During the last half of the movie, it's a matter of discussion if it was Vesper or Mathis who informed on Le Chiffre about his "tell" (give-away when he was bluffing). But it could just as easily have been a trick that the latter had planned all along - it didn't have to be either of the other two. After all, we're talking world-class poker players; why would it ever have been that easy to see through Le Chiffre's game?
Chosen answer: Le Chiffre operates as the banker for Mr White's entire organisation. The Ugandan is only one of many individuals and groups for whom Le Chiffre provides financial services; killing him does little to solve the problem of the missing money. Plus there's the question of trust - if Le Chiffre can't keep the money safe, then Mr White's organisation have no use for him and, as we see in the movie, will readily eliminate him. Le Chiffre's desperate to recover the money to prove his trustworthiness and save his own life.
Tailkinker ★