Well that's another teaching that needs reformed. Russell taught that most (if not all) humans would be saved. He was nearly a universalist. That's what we need to get back to.
It was (of all things) the Great Crowd doctrine that made their salvific model exclusivistic. Prior to that, they were perfectly okay with the idea that "good people" in other faiths would be saved.
Fast forward the clock nearly 83 years and the Great Crowd doctrine is in serious, serious trouble. Who knows? Maybe Russell's more benign view would be a way out of the theological cul-de-sac they've walked into