To your first question, I would have to say no, because a threat of violence (even if backed with a promise) is still just words. One step further, if that threat was then followed by the person punching you in the face, I do not think it is moral to kill (disproportionate reponse...one can only morally kill another human if the person is in danger of being killed himself). If a gun is being drawn, now the situation has shifted to life-threatening and one has a right to protect life (so admitedly, we get into difficult territory delineated exactly where the threat against life precisely occurs, I think this area is ripe for debate and certainly different people perceive threats in varying degrees).

To your second question, essentially my answer above applies although now, with multiple people acting with varying threat perceptions the entire situation has become more difficult to summarize (if that makes sense?)

In the rape example, if the person is actually doing the act, witnesses to the act can morally take increasingly aggressive action toward the perpetrator to the point at which the violation ends. Again, the verbiage "raping until death" consitutes a threat, and is not the same as the act of killing, therefore it is not moral to automatically kill a human in the process of raping (even though it may feel like the "right" thing (emotionally) to do). The rapist should be stopped and penalized proportionately (certainly another area of discussion).

All of the above is not to be lenient on violence shitbags that want to harm innocent people. These individuals should face penalty proportionate to their crimes, but I do not think pre-meditated murder by uneffected agents acting on behalf of the state is proportionate. Additionally, given our highly flawed/corrupt legal and political systems, we need to be careful not to use the mechanism of state-sanctioned violence to kill innocents that manage to get caught-up in the someone elses' crime drama. I always come back to the thought, "What is the maximum number of innocent lives lost (to be clear - false conviction ending in death penalty) I am willing to accept before deciding that the death penalty is not a moral choice of state-sanctioned penalty?" I always land on 0 for this question.