The title says it all really, but I think that since the battery is disconnected there is now an 'open circuit'. I know that charge can only flow if the circuit is complete (closed).
But the part that puzzles me here is, what is there to stop the electrons from the negatively charged capacitor plate 'flowing back' to where the negative terminal of the battery was located before?
Update:
Answers so far seem to indicate that I am asking 'where' the charge would go if the circuit was closed again (after the battery was disconnected) – by means of completing the circuit with a piece of metal or even yourself. This is not what I am asking; I am asking where the charge would go if the circuit was left open (still with no battery connected).
I have added a schematic below to clarify what I am actually asking. But put simply, would the charge stay on the capacitor plate(s) or would there be some 'leakage' or 'backflow' of charge away from the charged plates?
Best Answer
The charge won't go anywhere and the capacitor will remain charged until you short the plates of the capacitor. Where there was once a battery terminal there is now an insulator and that stops the electrons.
Also, the terminal will be made of metal that has a negligible capacitance so can't store significant amounts of charge.
And there is no net charge taken from the battery. The battery will push electrons from one of the capacitor's plate to the other.
Regarding your update: A theoretical perfect capacitor will never lose any volts. A real capacitor will always lose volts because air has some conductance and so does whatever dielectric is used to separate the plates. Even though a practical capacitor will lose volts, the loss may be small enough that it won't discharge in years.