Anything can break due to all kinds of differing reasons. Some have been mentioned here. The question was are today's Leupold Variable scopes reliable? An adjunct inference question was are fixed power scopes more reliable? I think it is pretty safe to state that as a rule, any fixed power scope is more reliable than a variable one. I suspect the answer to the latter question is yes as there are simply more things that can and sometimes do go wrong in a variable scope than a fixed one. Having said that, perhaps a better question would be how reliable is reliable enough?
At one time or another, I've used just about every scope available, from the glamour European scopes to the bargain basement models and about everything in-between those extremes. I've had a few that didn't last long, usually one of the lower price models. Mostly though, they have all done pretty well. I have more experience with Leupold scopes than all other makes combined. I haven't counted lately but I'd guess that in my safe at this moment there are about twenty-five rifles with Leupold scopes mounted on them. One of them is a FX-6X and the rest are variables of one type or another, mostly in the 2-7 or 3-9 power range. In addition I have a couple Zeiss variables , perhaps a half dozen Denver Redfield scopes, all variables, two Schmidt & Bender fixed 6X scopes, a US Optics variable, A Bushnell variable, and probably another make or two mounted. I've used Swarovski variables, Meopta variables and naturally Weaver scopes both fixed and variable, Nightforce variables, and one Kahles 3x9 variable I just remembered.
I don't recall ever having a failure with a fixed power scope, and off the top of my head, I can't recall ever having a variable scope fail that could be attributed to the fact that it was a variable and not fixed power scopes.
All in all, it seems to me that the scope manufacturers and particularly Leupold do an amazing job producing reliable scopes. If I had to answer the question, is a fixed power scope more reliable than a variable power one, I have to answer yes, it is. However my experience tells me that we'd be picking nits to the extreme. TT
