I don't put a single thing past pat riley. The man brought us Zo and Hardaway, then Shaq to compliment Wade, then the big three. His moves get bigger and more bold with each iteration. The players union's endorsement is irrelevant. If the four take 13 million a year they would have 7 mil plus a mid level to fill out the team. Its their prerogative to do so. Adam silver also would have no way to stop it--since all 4 would have to opt out and therefore become free agents with the freedom to do what pleases them. I also don't think the team will have that many issues regarding 'figuring' it out. They would likely adopt the SA method of playing starters only 30 or so minutes. Wade could keep on his maintenance program and Lebron wouldn't be burnt out. On top of the fact that Carmelo is already an established 3 point shooter and both Bron and Melo would space the floor for each other in a way that Wade never could. The heat also have a first round pick in this years draft (26th) for the first time in 4 years they could use to help the PG/C voids. If it wasn't a possibility you wouldn't be seeing it all over twitter and the sports websites.
Now wether it'd be good or bad for the league… not sure. The big three was a pretty huge financial and attention boost to the league. It had the NBA front and center on all sports news shows all the time. Would it be any different than when Jordan won his 6? or when the Celtics and Lakers were dominating in the 80s?
Ultimattely i get why you guys are all hoping it doesn't happen. But as a Heat fan you can imagine why i hope it does.