If by argument from ignorance you mean the wikipedia definition that "It asserts that a proposition is true because it has not yet been proven false (or vice versa)" then the answer depends if your talking meta-physically, i.e. reality, or practically, i.e. whether or not you would be justified in believing a proposition.
For meta-physically, it is never valid. Things are true or false regardless of whether someone has proven it to be true or false. For example, water has always been composed of 2 hydrogen molecules and 1 oxygen; it doesn't whether or not it's been proven true or it's negation false.
Practically, it can be valid. A classic example is "innocent until proven guilty."
For your second question, I'm assuming that when you say you "do not know that I am seeing it" you mean that you don't know the definition of elephant. In that case, it's not really a matter of truth but a matter of two people not understanding eachother. If you mean that you don't know whether or not you are seeing whatever the thing is, that's impossible. People are always aware of what they are seeing because they are seeing it; whether the thing exists in reality is a different question.
For your third, yes you can die even if you don't know it. Just because you didn't predict something doesn't mean it won't happen. For example, if someone sneaks up on you and stabs you, then you got stabbed; it didn't matter that you didn't know it was going to happen, or even that you don't know what stabbing is.