Based on the fivethirtyeight dataset (and hand-analysis of 2016-current), suggestions are that the Pacers became the 79th series loser to outscore the series winner in an official playoff series (1 of those is a BAA playoffs matchup in 1947... there were also 8 ABA matchups, but those are not officially recognized as NBA data).
However, the series marked the greatest disparity in 59 years, way back since the (St Louis) Hawks returned the favor to the (Minneapolis) Lakers.
Here's the ranked list as of this date (May 6, 2018):
1956: MNL Lakers lost to STL Hawks 1-2, but outscored by 56 points
1959: STL Hawks lost to MNL Lakers 2-4, but outscored by 43 points
2018: Pacers lost to Cavileers 3-4, but outscored by 40 points
1990: PHO Suns lost to POR Trailblazers 2-4, but outscored by 34 points
1982: BOS Celtics lost to PHI Sixers 3-4, but outscored by 33 points
1976: GSW Warriors lost to PHO Suns 3-4, but outscored by 29 points
1958: BOS Celtics lost to STL Hawks 2-4, but outscored by 27 points
1987: DET Pistons lost to BOS Celtics 3-4, but outscored by 26 points
2015: LAC Clippers lost to HOU Rockets 3-4, but outscored by 22 points
1981: PHO Suns lost to KCK Kings 3-4, but outscored by 19 points
1976: PHI Sixers lost to BUF Clippers 1-2, but outscored by 18 points
1981: MIL Bucks lost to PHI Sixers 3-4, but outscored by 18 points
1988: DET Pistons lost to LAL Lakers 3-4, but outscored by 18 points
1996: UTA Jazz lost to SEA Thunder 3-4, but outscored by 18 points
1974: DET Pistons lost to CHI Bulls 3-4, but outscored by 16 points
1984: LAL Lakers lost to BOS Celtics 3-4, but outscored by 16 points
1990: SAS Spurs lost to POR Trailblazers 3-4, but outscored by 16 points
1973: MIL Bucks lost to GSW Warriors 2-4, but outscored by 15 points
1995: SEA Thunder lost to LAL Lakers 1-3, but outscored by 15 points
1951: SYR Sixers lost to NYK Knicks 2-3, but outscored by 14 points
1972: MIL Bucks lost to LAL Lakers 2-4, but outscored by 14 points
2013: BRK Nets lost to CHI Bulls 3-4, but outscored by 14 points
1979: PHI Sixers lost to SAS Spurs 3-4, but outscored by 13 points
2000: POR Trailblazers lost to LAL Lakers 3-4, but outscored by 13 points
2005: DET Pistons lost to SAS Spurs 3-4, but outscored by 13 points
1978: MIL Bucks lost to DEN Nuggets 3-4, but outscored by 12 points
1990: CLE Cavaliers lost to PHI Sixers 2-3, but outscored by 12 points
1963: LAL Lakers lost to BOS Celtics 2-4, but outscored by 11 points
1988: ATL Hawks lost to BOS Celtics 3-4, but outscored by 11 points
1991: BOS Celtics lost to DET Pistons 2-4, but outscored by 11 points
2000: IND Pacers lost to LAL Lakers 2-4, but outscored by 11 points
2011: ORL Magic lost to ATL Hawks 2-4, but outscored by 11 points
1995: NYK Knicks lost to IND Pacers 3-4, but outscored by 10 points
2016: Pacers lost to Raptors 3-4, but outscored by 10 points
1956: BOS Celtics lost to SYR Sixers 1-2, but outscored by 9 points
1962: CIN Kings lost to DET Pistons 1-3, but outscored by 9 points
2000: MIL Bucks lost to IND Pacers 2-3, but outscored by 9 points
1968: STL Hawks lost to SFW Warriors 2-4, but outscored by 8 points
1974: CAP Wizards lost to NYK Knicks 3-4, but outscored by 8 points
1994: CHI Bulls lost to NYK Knicks 3-4, but outscored by 8 points
2004: SAC Kings lost to MIN Timberwolves 3-4, but outscored by 8 points
2008: CLE Cavaliers lost to BOS Celtics 3-4, but outscored by 8 points
2003: POR Trailblazers lost to DAL Mavericks 3-4, but outscored by 7 points
2004: DAL Mavericks lost to SAC Kings 1-4, but outscored by 7 points
2006: LAC Clippers lost to PHO Suns 3-4, but outscored by 7 points
2016: Thunder lost to Warriors 3-4, but outscored by 7 points
1952: BOS Celtics lost to NYK Knicks 1-2, but outscored by 6 points
1980: MIL Bucks lost to SEA Thunder 3-4, but outscored by 6 points
1998: ATL Hawks lost to CHH Pelicans 1-3, but outscored by 6 points
2009: MIA Heat lost to ATL Hawks 3-4, but outscored by 6 points
2016: Clippers lost to Trailblazers 2-4, but outscored by 6 points
1979: SAS Spurs lost to WSB Wizards 3-4, but outscored by 5 points
1986: PHI Sixers lost to MIL Bucks 3-4, but outscored by 5 points
1994: NYK Knicks lost to HOU Rockets 3-4, but outscored by 5 points
2012: MEM Grizzlies lost to LAC Clippers 3-4, but outscored by 5 points
2013: SAS Spurs lost to MIA Heat 3-4, but outscored by 5 points
1955: FTW Pistons lost to SYR Sixers 3-4, but outscored by 4 points
1976: WSB Wizards lost to CLE Cavaliers 3-4, but outscored by 4 points
1994: SEA Thunder lost to DEN Nuggets 2-3, but outscored by 4 points
2016: Spurs lost to Thunder 3-4, but outscored by 4 points
1953: ROC Kings lost to FTW Pistons 1-2, but outscored by 3 points
1969: LAL Lakers lost to BOS Celtics 3-4, but outscored by 3 points
1982: SEA Thunder lost to SAS Spurs 1-4, but outscored by 3 points
1984: DET Pistons lost to NYK Knicks 2-3, but outscored by 3 points
1990: BOS Celtics lost to NYK Knicks 2-3, but outscored by 3 points
2007: PHO Suns lost to SAS Spurs 2-4, but outscored by 3 points
2012: DEN Nuggets lost to LAL Lakers 3-4, but outscored by 3 points
2015: SAS Spurs lost to LAC Clippers 3-4, but outscored by 3 points
1950: SHE Redskins lost to INO Olympians 1-2, but outscored by 2 points
1992: GSW Warriors lost to SEA Thunder 1-3, but outscored by 2 points
2002: SAC Kings lost to LAL Lakers 3-4, but outscored by 2 points
2014: HOU Rockets lost to POR Trailblazers 2-4, but outscored by 2 points
1947: STB Bombers lost to PHW Warriors 1-2, but outscored by 1 points
1951: INO Olympians lost to MNL Lakers 1-2, but outscored by 1 points
1982: PHI Sixers lost to LAL Lakers 2-4, but outscored by 1 points
1989: HOU Rockets lost to SEA Thunder 1-3, but outscored by 1 points
1993: IND Pacers lost to NYK Knicks 1-3, but outscored by 1 points
2002: IND Pacers lost to NJN Nets 2-3, but outscored by 1 points
2006: WAS Wizards lost to CLE Cavaliers 2-4, but outscored by 1 points
(Note I cannot absolutely ensure the lack of errors... the dataset doesn't indicate where playoff series start and end.... which happened to be a problem in the 56 season, when MNL and STL actually played 4 playoff games in a row.... but turns out the first was a division tiebreaker! I fixed that issue, but there could feasibly be similar small errors, either in computation, or in the dataset itself)
(Apologies for team monikers like Seattle Thunder, but it's how the set was laid out to maintain franchise records)
And for those wondering:
- 2016 and 1990 hold the record of 4 series to wind up this way (no surprise since more teams make the playoffs in the modern days!)
- Only four years since 2000 have not had this occurrence happen.