The Heat won't lose three straight. I suspect they'll steal one in San Antonio much like the Spurs stole Game 1 in Miami.
Also, only four teams in the history of the 2-3-2 format have won all of the home middle games (Detroit 2004, Miami 2006, 2012). Houston in 1995 swept Orlando and didn't play Game 5. I think Miami is too good to lose three straight.