There is a lot of examples were the Big Brother Mentor (unlike the more generic Obi Wan) does not die at all, and even sometimes gets a character development/maturing factors for himself within the story, in parallel or despite the Hero´s development, often pointing to very different objectives than those of the hero, more accord with his "grown-up" status.

In my opinion, this further diferentiates this trope from the Obi Wan, as the Obi Wan is a fully developed character whose sole mission is to guide the Hero, while the Big Brother Mentor is a character that still have things to do in the world by himself, aside from being mentor.

When this character actually dies, he often gives the Hero the obligation to fullfil HIS mission, BESIDES the Hero´s mission

Examples are Racer X from Speed Racer, Holland form Eureka Seven (the granpa of Renton also from Eureka Seven could count), The Golden Saints for Saint Seiya, Quattro Bageena in Gundam Z, or the X-Men characters when they appear in their junior series (like New Mutants, X-Force, X-Generation and the like). I think that the point of NOT dying and get character development and growing maturity by him/helself is very important, enough to be mentioned not only as a "collection of exceptions" of the Big Brother, or even to create a complete separated sub trope (that could be called the "Badass Brother" "Grump" (for grown-up) or the like.