The 2015 playoffs for the Dallas Mavericks were largely a disappointment, the frenetic play of on Al-Farouq Aminu aside. The Rondo trade was an unmitigated failure, as the player brought in to hopefully launch a scoring juggernaut into title contention barely made it to the second game before he was summarily banished. The reasons for pursuing this trade have been covered ad nauseum, and whether it was ultimately worth the risk is a topic for another piece.
The trade has lingering negative effects beyond the playoffs flame-out, as Jay has pointed out. Management hoped and expected Rondo to re-sign for the long-term when they brought him here, and alongside Parsons and Nowitzki (and likely Tyson when he was re-signed as well), the core of the team would be set for the next few years.