I wouldn't recommend writing bad reviews unless you actually attended an event that East Coast Event Group provided the DJ, photo or video services. I have heard of cases where people who wrote negative reviews on Yelp have been sued.
However, merely stating that Mike Rossi works at Easy Coast Event Group is not libel at all. Its a fact. I think runners who are aware of this incident will never book any of their services and will advise friends and relatives who get engaged to avoid them. And I wouldn't be surprised it that is already the case within the teaching industry. I would think most people know somebody who works in the school system, so the word is probably already out.
But I doubt Mike will feel the effects of his actions for at least a few months. Weddings are planned at least year in advance and all the major vendors (hall, DJ, photo) probably gets booked that far in advance. But in a few months he may do a year over year review of his bookings and realize that his schedule is looking a bit lighter.
If his boss was smart he would just cut him lose right now. He is going to be a huge liability to a company that probably has some good people working for them.