Portland is a pretty good destination for a lot of NBA players. But not a top destination. Call me insecure, but the risk of letting potentially great players become a free agent always worries me. Lock them up long term until they get used to the rain. (It takes about 8-10 years.) Sure we end up over paying a little. But that is what it takes.
There is no risk of losing him, as we can match whatever offer any team gives him. We can, however, potentially risk the chance of overpaying him.