Would metal leaf electroscope experiment work if the terminal were made out of an insulator?
No it would not work because an insulator stops electrons from moving from moving to atom to atom so there is no way to get a charge to the metal leaves
when a substance is electrically charged it has either too few or too many electrons. when the electroscope is brought near a charged object the electrons 'jump' if the substance had too many electrons then the extras would 'jump' to the electroscope giving it a negative charge if the substance had too few electrons then the electrons from the electroscpe would 'jump' to the substance, giving the electroscope a positive charge
Charge would flow from the charged electroscope to the initially uncharged one, until the charges are equal on both. At that point, the potential on both ends of the wire would be equal, there would be no voltage across the wire, and no more current would flow. Both electroscopes would then be charged, with charge of the same sign, and with half as much charge as the initially-charged one had.