It depends on your reason for stipulating that you would be willing to self-terminate at the age of 1,000.
Good question. I wasn't actually saying that I would self-terminate so much as that I would be willing to take the risk, although I don't know what that would entail.
My point is that if there is an afterlife, death wouldn't be such a bad thing and the reason to want to live forever in the current reality be gone. The dilemma is how will I ever know that there is an afterlife unless I "die" (which technically wouldn't be death if I lived on in some supernatural reality)? If I can't know one way or the other, why would I want to risk death since it might be the loss of life, without an afterlife.