With a bit of clarification from
@PMatic, here's why the Heat pretty much have to let Whiteside walk.
1. Even if Chris Bosh were to retire, they won't get cap relief this upcoming season, and all signs point to Chris Bosh is going to play next season.
2. If they traded McRoberts (won't be too hard)... The team of Bosh, Dragic, Winslow, Tyler Johnson & Josh Richardson + 5 cap holds gives them a maximum of $45.689mil in cap space to re-sign Wade & Whiteside.
3. They do not have Whiteside's Bird Rights, so his deal has to be done under the cap. He will command $21mil. Riley will not get him to take less. He's a guy who only has $2mil in career earnings at 27. Maybe you can get him to sacrifice $5mil over 5 years, but you are not getting some huge discount on him.
4. They do have Wade's Bird Rights. So they can go over the cap to re-sign him. BUT in order to keep his Bird Right's, they have to hang on to his cap hold. His cap hold is $30mil. So they pretty much have to sign Wade before Whiteside if they wanted to keep him, in order to get off of Wade's cap hold, and open up the required space for Whiteside.
If they're luck Whiteside & Wade is $35mil ($21 HW + $14 DW)
But what is far more likely is $41mil ($21 HW + $20 DW)
That leaves between $4-10mil in cap space, not enough to really get a great player, maybe a quality 6th man.
5. They could open up max cap space if they unload Dragic for nothing. But that's then a team in desperate need of a PG. If you add Mike Conley for Goran Dragic, did you really accomplish much?
Keep Wade, Dragic & Whiteside... Or trade Dragic and keep DW & HW, it's a team that is barely 6 players deep. Cannot win a title with that
So unless Riley wants to sit on the same team for the next few years, he has to let Whiteside walk in order to try and make a big splash.