Tatiana Ponomareva writes from the Nabokov Museum:

 

I checked a few available sources on Vengerov.
 Nothing specific - he most probably died from illness and paleolithic conditions of life in
 Petrograd in 1920. Chukovsky mentions
 him discussing "the formal menthod"  with his Pushkin seminar students even on his
 deathbed.
 The general explanation that comes to mind: we know Vengerov
 as a staunch "narodnik", a
 Chernyshevsky follower. "Literature is not just an art, it's a pulpit".
 Also,  Vengerov was known  for the amazing quantity of his literary output.
 So maybe VN imagined him writing on incessantly for a hundred years,
 well into the decades of terror, outliving Stalin,
 editing other encyclopedias, other huge collections, this time of
"socialist realism" writers?
Unless there was something specific he learned fom Yakovlev.

 Tatiana Ponomareva