Suppose I first charge a capacitor so that one plate is positively charged and another negatively. Now I remove the charging source and ground only one of the terminals say negative terminal, will there be a net positive charge in the capacitor that can be detected by a pith ball? Can a capacitor be used as static electricity generator?
When you connect the negative terminal to ground, why would the negative charge flow anywhere? It has to exist somewhere, and it might as well be close to the positive charge on the other capacitor plate.
You could also consider a very similar scenario in which you connect the negative side to ground before disconnecting the charging source. In this case, when you disconnect the source no charge will flow.