So what is left? It is the true realization of Śūnyatā, or Ultimate Truth, a realm in which “reason is used to destroy itself” The above is a quote from 'Humphreys, Christmas.  Buddhism: An Introduction and Guide'p145. 

Is it true that the main aim of Buddhism (Mahayana) is for reason to destroy itself? 

That really sound too colorful and worst than nihilism itself
Good question. That's a rather crude statement, albeit a nice first approximation.

More precisely I would say, the aim is to clearly see the Value, the Limitations, and the Danger of having subjective experience entirely subsumed within a framework made of models and concepts (taken at their face values as being the reality itself, aka "reified"), to see how this mistake is universal, inevitable, and intrinsic part of sentient life, to see the mechanisms behind arising of said conceptually conditioned experience, and finally to master the practical means of manipulating said mechanisms towards liberation from the confines of said framework to the reality of authentic suchness.