These eras in general are arbitrary. It wasn't as if classical antiquity was just declared as being over, nor is it possible to really put a date on when what we see to be the classical world as "ending." It isn't akin to something like the "Tudor period" in English history, which can easily be dated as starting with crowning of Henry Tudor as King Henry VII in 1485 and ending with the death of Queen Elizabeth I in 1603. Any year purported to be the end of classical antiquity will have to be chosen for some reason that is arbitrary.

As /u/cyaxares mentons, the death of Hypatia is a very evocative story that can be used as a metaphor for greater trends. One can read the death of Hypatia as being a representation of the death of cosmopolitan, classical philosophy at the hands of religious zealots. For people who promote or subscribe to the idea of a dichotomy between an enlightened age of antiquity followed by a superstitious age of darkness, Hypatia is the perfect martyr.

Given that Hypatia was far from the last Greek philosopher (even pagan philosophy survived for a bit longer), and given that the clash between religion and philosophy is something that is often exaggerated, I haven't seen any recent historian claim that the death of Hypatia was "the end of classical antiquity." Those who do mention it generally say something along the lines of "the death of Hypatia can be seen as symbolic of the end of classical antiquity."

Such end dates are always chosen for their symbolic value.

Of two historians who agree on the basic date of the end of classical antiquity one might choose the death of Theodosius in 395 (last emperor to rule the whole empire, after his death things got chaotic) and the other one the death of Hypatia in 415. And by doing so they would suggest two very different narratives to you.

The attraction of the death of Hypatia is that as a female philosopher she can stand in as the personification of Philosophy herself (who gets brutally murdered by Christianity).
One thing she certainly wasn't is the last pagan philosopher teaching in Alexandria (e.g. you have Olympiodorus ~150 years later).

That being said afaik the most common date for the end of classical antiquity in the East is 529 CE (again chosen for symbolic value), the year in which Justinian closed down the Academy.