Music evolves, the instruments that were popular hundreds of years ago have had varying degrees of longevity. Sometimes due to changes in taste/ fashion and sometimes by being superseded. The key to the survival of any instrument is linked to those two factors. However, even if they are generally out of fashion or superseded they will still be used by a core of enthusiasts of niche groups. So the Bass guitar is likely to survive in some form or other for a long time, it's popularity and mainstream appeal will be determined by factors in the future that are very hard if not impossible to predict.