Lol, not happening. Riley doesn't trade key expiring players when his teams are contending. Also, the Heat will have the cap room to re-sign him if they go that route. They're under the cap same as everyone else, including Wade's cap hold.
Also, Whiteside makes the minimum. Pretty much any player the Heat acquire to replace him would have a higher salary, which would increase the tax bill they owe. Considering they're giving away draft picks to owe less money, it seems unlikely they'd downgrade talent to spend more.