We'd literally have to sell him for more than £1.5m to make any profit on the extended period of wages we'd pay if he's on that much. Makes zero sense extending the contract under the pretence of making some money on him.
If it's true that he's on around £30k per week that has been mentioned on here then we'd be better off just letting him go. Say we extend him and then no bugger wants him or he gets injured again and we can't sell him. We'd be stuck with his wages for another year.