The 2012 Celtics lost to the Miami Heat in Game 7 of the Eastern Conference Finals. I believe the Celtics were up by as much as 11 points in the game, but the theme of the series always seemed to be that the Celtics ran out of gas down the stretch.
During the offseason, Ray Allen of course took his talents to South Beach but the C's had already signed some much needed bench help in Jason Terry. They also added some serviceable vets like Jeff Green, Courtney Lee, Leandro Barbosa and a rookie lottery-level talent in Jared Sullinger.
With Ray Allen being the only major piece lost, the Celtics looked to be a better team than the 2012 bunch. Doc Rivers even made comments in training camp telling his team that "He felt good about them", and that if the league was 10 vs 10 "They'd beat everyone.", speaking to the added depth and relief that the aging starters would have.
Things just never worked out that way though. The team saw Rondo, Barbosa, and Sullinger go down with season ending injuries, and lose in the first round to the New York Knicks.
Had all personnel been healthy, could that team have beaten the Heat?