1. Do you know when the club offered him a new deal? How much? Unless you have inside information, nothing is 'clear'
2. The injury could have been an opportunity to get him to extend his contract for another year
3. We could have brought in another player using the fee, and freed up wages, so it wouldn't have been a case of being a centre back down
4. Dickie isn't as good a player with as much potential as Nelson. But yes, if he only has a year left, makes it clear that he will not sign a new contract no matter what, and a club comes in with a decent bid I would sell him - wouldn't you?