According to a forum post, the games will go offline on June 7, giving players two more months to keep playing. The post also claims that all three games "are no longer performing at a level in which they can continue to be supported," hence the decision to close them down.
Based on numbers from AppData, Pirates Ahoy has been on a steady decline in terms of players, but still currently boasts an audience of 275,000 monthly active users. Gangster City and Poker Rivals, meanwhile, are both hovering around the 90,000 MAU plateau.
The forums for each game will remain open for around a month following the closure of the games in June.