For example, the nominal date of the end of the Roman Empire in the west, 476 CE, was in no way the end of the Roman Empire, east or west. It is just a convenient date used by historians who need to pick a date for the history books and chose one when the city was occupied briefly by a Germanic warlord for failing to pay a ransom. The empire had certainly ceased to be very effective in the west long before this, and the senate continued to meet for long after.
So when we review the end of the Los Angeles visual effects community, we may as well pick an arbitrary date, but one that is at least symbolic, just as with the nominal date of the end of the Western Roman Empire.
I propose that this date is last week when Sony Imageworks announced that it was moving its headquarters to Vancouver, Canada. In fact, there is still going to be some people working at Imageworks in Los Angeles, including Ken Ralston, ASC. And there are other visual effects companies such as Digital Domain that seem to linger on as well as many of the smaller shops.
In fact, the Sony's announcement, which can be read here in the Hollywood Reporter, is confusing. Are they moving people from LA to Vancouver? Or are they just not hiring more people in LA and hiring in Vancouver? It isn't clear. What I hear indirectly is that they are moving people up north, however, or maybe perhaps they are just expecting people to move up north on their own. Like I say, it isnt altogether clear.