Seems that there have been pressures from Consob, the Italian entity that vigiles on Companies that are on the stock exchange, and also from the Italian Procura, the prosecutor's office.
So, during the last board meeting they discussed harshly and finally Elkann decided to remove the whole board.
They resigned but kinda forced to.
What can happen next:
For what Consob concernes, if the financial irregularities are confirmed and proven, there can be fines and even jail (depends on how intentional were these irregularities) for the former board's members.
Consequently, another trial will start for unfair and unethical conduct from the Italian Sport Court, more or less what happened in 2006 for Calciopoli, ended with their relegation.
On the other end, their are under investigation for mafia infiltration in their supporters groups and Camorra's affiliation, since Agnelli has been found repeatdly having direct relations with their members.
Bad times for them, good times for the whole football movement in Italy.