Sivert Andreas Torbersen Rambraut

Hello Dear Friends. I am glad to see many of you still here and I am still working on my family history but spending less time these days. A mystery that has been nagging me is whatever became of Sivert Andreas Torbersen Rambraut. Born June 23, 1849 in Trondheim, and confirmed October 11, 1863 at Domkirken in Trondheim. In 1865 he is listed in the National Census in Trondheim with his sister Ingeborg and his parents, Anders and Sigri Rambraut. this is where we lose him...... In 1865 or early 1866 Sivert's sister moved to Vardo in Finnmark where she married. I am in possession of a letter that Sivert wrote to his sister on May 30, 1866. after that nothing. Sivert cannot be found in the 1875 census and he is not listed as a sponsor on any of his sisters children's baptisms. I conclude Sivert died most likely shortly after 1866 but before 1875. I have looked at death records in Trondheim and emigration records thinking he might have moved and died somewhere else. This is a brick wall for me and thought I would ask one more time in here if anybody had any other thoughts. thank you.