I think officiating will be huge. Indiana's strength is in their physical style of play (particularly inside), and it worked against the Knicks, but I don't know if the refs will be as permissive (at least in big plays, down the stretch) against Miami.
Those drives where Melo and JR got bothered or stopped by Hibbert and other Indy big men and the refs didn't call fouls acknowledging verticality in the jump... maybe against LeBron and Wade those plays aren't called the same..
Outside of that, Indiana's offense (or lack thereof) will be the deciding factor. Miami is MUCH more consistent on offense, and they are also very good defensively (trapping, rotating, playing pressure D), so if Indiana wants to have a shot at this they need to have their shooters sharp, can't afford to miss gimmies, FTs or turn the ball over, have to make sure the ball keeps moving and that they are taking good shots. All easier said than done, but all necessary.
I think it's Miami back to the finals, and probably in 6. Maybe 5.
"The first time I ever saw my uniform hanging in the locker I put it on right away, and it just felt like I was putting on golden armour. From that day forward, I just called it 'the golden armour', it just felt like there was something mystical and magical about it" - Kobe Bryant.