If people who follow would instead follow @UnfollowTrump on Twitter then we might be able to get an accurate count.
I'm in tech, and I'm afraid I'll have to disappoint you terribly: if this actually happened and led to a significant fall in followers, the more fanatical ones would just set up fake accounts to make up for it. In no other presidency would this ever have happened, but it would in this one because SM followers are now apparently a source of political legitimacy.
It's ridiculously easy to set up, too. I keep on wanting to set up a twitter bot that replies "it's going to be okay, my father never loved me, either" to whatever Uday, Qusay or Barbie tweet.
...
Talking tech, though: how insane is the fake email story? I can't believe the hoaxer even got the security guy to reply. My firm virtually spams us with phishing test mails and mandatory trainings; I would have expected the WH to be at least as cautious!