i've haven't thought about this scenerio. if joy division progressed, and assuming they gathered more success, i think the press would continuely think of JD as ian's band. in a way, they still do. i think ian would have been pissed over that and refused to do interviews. that is one prediction. i don't know much about ian (haven't gotten around reading that debbie curtis book), so it's hard to say where the band would go. i assume they'd still progress into an electronic band, cuz that was what ian was interested in.
and if barney died that young, i doubt people would remember him very much in the public or in music history. he wouldn't have had the opportunity to show his potential. joy division were not very well established, and barney was still timid on stage, and he could have easily been overlooked back then.
when you think about it, the story of joy division is usually seen as the story of ian curtis. he's the focal point of the band, at least in most music enclopedia bios he is.