Well, regardless of the big men they could have signed, there are also two issues.
First, it is not a given that Mayo would have resigned. He would have been fighting for the starting spot with Bradley last year, and if he had lost out, he might have walked, in order to find a situation where he could start and showcase himself for a bigger contract.
Second, the C's nearly made the finals last year, and based on previous history with big, midseason trades that affect the teams core, this team might have fallen apart down the stretch, had they made the trade, and not had that run. That would be a steep price to pay.