The Pacers can still technically be the #4 seed in the East if they lose tonight's critical home game against Boston, but it's not a very realistic chance. Indiana needs the victory to break even in the head-to-head series with the Celtics (currently 2-1 Boston) and go a game up with just two to play. That would create a scenario where the Pacers would have to lose at least once and the Celtics would have to win out.
INDIANA (after tonight): Nets, at Hawks
BOSTON (after tonight): Magic, at Wizards
If the Pacers win tonight and the two teams finish tied, Boston would be the #4 seed via the second tiebreaker (conference record).
If the Pacers lose tonight, they would have to finish ahead of the Celtics in the standings, meaning they'd need to win out while Boston lost their final two games.