Re-cone if you want to restore the combo
Putting in a more expensive driver and not adjusting for the cabinet tuning could be a waste of money - or you might get lucky.
Or buy a cheap replacement if you want to get it working enough for a practice amp http://www.mcmelectronics.com/produc...-2952-/55-2952
You might get lucky here too and it may work fine. Or it may not.
Either way you can play with the porting for better performance of the driver.