It's always disappointing to lose a good player at the end of his contract but if he's moving on to better things while his stock is high then it's understandable, so long as he isn't moving to a league rival and we've offered him the best we could to retain him. That said, if we had kept him and got promoted, he might've renewed his contract here.
The real issue I have with your stance is you're rejoicing such a paltry amount received. Sheridan will probably blow that 85k trying to replace him throughout this season, Bobby Reid for example, who won't be here next season either. So financially we're no better off but we're a goal-scoring midfielder short. Surely you can see why it would be better to keep a settled player on top of his form under these circumstances?