I don't think so, severity of abuse exists on such a wide spectrum. I've definitely heard of cases where someone kills their abuser or a loved one gets revenge on behalf of the abused and I privately support them in my own mind. But to say that's a right is something else entirely

If they're really stuck and can't get any help, exhausting all other options and it's a life or death situation, yeah.

No - but I believe the legal system can effectively take their livelihood and access to life away.

No. Not an inherent right.

In case it happens in self defence ....

I wouldn't make a law saying that, but I wouldn't say the opposite either. I just imagine the world would lose some famous or important men people if that became reality.

I don't think there are any natural/inherent human rights. If there were, then they wouldn't be able to be violated, or else what would it mean to have a natural right? Rights are things given to us by law. And the law doesn't allow vigilante/revenge killings. So no, we don't have that right. Should we have that right? As much as I like hearing about bullies and other kinds of abusers being harmed or killed, I know that's wrong, and philosophically I don't believe in vengeance/retribution, so I'd say no. https://philosophy.inhahe.com/2017/02/05/is-hatred-ever-truly-justified/