We don't know how many of them survived and how many of them are loyal to the Council. As far as we know, Justin could have been one of those apprentices. We simply do not have enough information.
Justin's master was Simon. That much, at least, was mentioned in Summer Knight.
The rest, though, yeah, you're right, there's not much grounds to speculate on. Given the skill set Ebenezar would be the ideal teacher for, I'd guess quite a few of them probably wound up in the old guard of the Wardens and/or the 'brute squad' at Archangel, so I can buy most of them being dead by the story era. But out of a pool that large, there pretty much have to be some still alive somewhere.
Likely a few on the grey council, which would explain Eb compartmentalizing Harry from even meeting them outside of that content - better operational security if he doesn't know them at all.