Did Pythagoras' school collapse because of their discovery of irrational numbers? Pythagoras believed that "all is numbers" and they maintained that all numbers can be expressed as a fraction, then Hippasus (maybe) showed some numbers cannot be expressed that way.  Pythagorus thought this idea was stupid and he had him killed, but this could not stop the eventual collapse of his school.
This question could be too subjective (I'll remove it if it is), but is this story untrue or too obscure to know owing to the secretive nature of his sect and its ancient nature?   
 A: See the SEP entry about Pythagoras : from ca. 570 to ca. 490 BCE, and the entry on Pythagoreanism :

Pythagoreanism is the philosophy of a group of philosophers active in the fifth and the first half of the fourth century BCE :



*

*Philolaus of Croton (ca. 470-ca. 390 BCE)

*Archytas (ca. 420-ca. 350 BCE).

Many other sixth-, fifth- and fourth-century thinkers are labeled Pythagoreans in the Greek tradition after the fourth century BCE. [...] There are nonetheless a number of thinkers of the fifth and fourth century BCE, who can legitimately be called Pythagoreans, although often little is known about them except their names. The most important of these figures is Hippasus [from Metapontum fifth-century BCE].

But we have to recorc also :

Aristoxenus (ca. 375- ca. 300 BCE) is most famous as a music theorist and as a member of the Lyceum, who was disappointed not be to named Aristotle's successor. In his early years, however, he was a Pythagorean, and he is one of the most important sources for early Pythagoreanism. 

This shows us that the school was "alive and well" during Aristotle's time (384–322 BCE).
Thus, I think it is not correct to speak of "collapse of his school".
A: The school did not collapse at all. They simply continued expressing everything in terms of natural numbers and proportions among them. As late as the 19th century, Leopold Kronecker sought to do much the same thing, incredible though it might seem to us. You are probably familiar with how one could express statements about rational numbers in terms of integers. You can similarly express statements about real numbers in terms of rationals, so from a strictly logical viewpoint you don't actually need them. For example, every time you want to say that your favorite number $b$ is less than the irrational $\sqrt{2}$, just say $(\forall x\in\mathbb{Q})(x^2>2\;\to\; b<x)$.
