I disagree. Flawed as his gamr may be Willie is an asset, if you let him walk for nothing you have to ask yourself can you do better with the money? Let him go field offers come back and forced a sign and trade and get assets for him or decide if you're going to just let him walk. At this point the Kings have 60 million in cap space and they can always clear more space if they had to buy revoking an offer to Willy.
Young players (Willie was a 3 year college player, so not the best comparison, but still), often blossom late. It will be bad if he plays well for some other team, but it will be worse if he does it and we don't get anything in return, after investing in him for four seasons.