Home teams are 100-24 in Game 7s in the NBA playoffs, so there is essentially a 75% shot that the Warriors are indeed going to make it to the Finals.
The NBA is trying to prepare in advance, especially because of the short turnaround, but SB Nation noticed they were already selling tickets for Game 1 of the Finals even before Game 7 started.
Someone must have alerted the Facebook admin because they tickets are mysteriously gone now.