nobody has ever given me "a number", but they SHOULDN'T be short-lived, based on the typical lifespans of other scorps, and to be honest, i think lack of proper nutrition is a HUGE part of the equation for most of the "hard to keep" species. sometimes even fish that eat well aren't getting what they need (i'm not just talking scorps here).
many years back, my first volitans lived for about 10 years, which is really only about half of what they should, and i attribute its "early" demise to poor nutrition. i fed it primarily frozen and freeze-dried krill, which is what was suggested to me by the LFS, but i digress. this was almost 20 years ago.
there are still plenty of folks who say that you can't keep SH alive in captivity as well, and we know plenty of peeps (incl. ourselves) who have no trouble with it, providing their nutritional and other "special" needs are met.
at any rate, we're hoping that a good, varied diet will result in our Rhinos being around for many years to come.