As has been said many times before it would have veen perfectly legitimate for the club not to offer Wyness a new contract given that he's not had the best of seasons, it would also have been acceptable to ask him to prove himself to between now and the end ofthe season with a view to earning a new contract.
What's not acceptable, on any view, is agreeing a contract unconditionally and then withdrawing it before it's signed.
For what it's worth, a contract for services does not require to be in writing and it seems to me that if Wyness was offered terms for a further two years and that offer was withdrawn then he my well have recourse to the civil courts or an employment tribunal.
Whatever anyone may think about the merits of offering Denzil a new two year contract and there are good arguments on both sides, what happened in fact is a disgrace.