Possibly, but I guarantee you that if Wade had left, Mickey Arison wouldn't have acted the same way either. Wade may not have been born here, but he's by far the most popular athlete in South Florida, and it would have set the franchise back 10 years (like when Shaq left Orlando).
But a letter that said "LeBron, thanks for the memories. We are now looking to the future, blah blah blah" would have been infinitely better than "Cleveland will win a title before the Heat do/LeBron's a coward and a quitter."