I wouldn't say trash but it's just unfortunate that their best player good injured and so when Mitchell went down, it's obvious that they will not go and win the series and as you have said, the Celtics should have swept them. And as expected, the Boston Celtics is already in the Eastern conference finals again, and waiting for their opponents, either the Knicks or Pacers.
As to their opponent, it's not certain yet because if the Pacers will take this to game 7, I'd say it's 50-50 even if the pacers are playing on the road.
Mavs steal another win on the road, it's time to close the game in 6. Actually, Mavs could have ended the series already if they were more careful in game 4.