I think the reason it's confusing is because it's literal AND vague, the reader is left to interpret the context for dying. Without the context I would interpret it as something like "I would not bet my life that my beliefs are right, because there is always a non-zero chance that they are." Although taking this too literally has problems too (what are the conditions and stakes for the bet?), I think it's a natural feature of the quote that the reader is invited to imagine a scenario where this makes sense.
I believe Russell's quote is mostly literal and you're simply misinterpreting it. Knowing the context helps, see https://quoteinvestigator.com/2016/03/07/never-die/
I think the reason it's confusing is because it's literal AND vague, the reader is left to interpret the context for dying. Without the context I would interpret it as something like "I would not bet my life that my beliefs are right, because there is always a non-zero chance that they are." Although taking this too literally has problems too (what are the conditions and stakes for the bet?), I think it's a natural feature of the quote that the reader is invited to imagine a scenario where this makes sense.