I just wanted to add here that this article (and Sophia's article) mentions that Sal died at an unknown time. In Season 4 Episode 1 "Yes, We Have No Havanas" Sophia says she hasn't showered with a man in 22 years. Dorothy quickly corrects her that Sal has been dead for 27 years. The episode aired in October of 1988, so it's safe to assume Sal died in 1961.
Golden Girls Wiki