The gemoro psochim 2b mentions only about a 'ganev' (stealthy thief) coming at night that one may kill the thief even if he is not sure this thief is about to kill him. What about if this thief came by day? Is he allowed to kill the thief even if he is not sure this 'ganev' would kill him if he doesn't get his money otherwise.
if somoene breaks into your house they are a threat to your safety and you may kill them. unless... they cower and show physically by submitting such as lying on the ground with their hands on their head or if they run away. If the thief submits or suns away they are no longer a threat and killing them would not be self defense anymore.