The old WAMs and P-4s will run under their respective ELS in SER or any other Zonal Rail Network until they live out their entire service life (May be 25-30 Years). Each of these electric locos cost around 1 Crore or more. Their (P-4s) manufacturing may stop by 2020 just like WAM-4s stopped in 1997 by CLW. These are extremely technical issues that IR doesn't let out so easily to common citizens like you or us may be due to security reasons etc. Try for an RTI nowadays since the new Central Govt of India has been in the process of appointing new CIC and CVC :-)