Remember even if these two trains runs separately, you cannot change their routes between TATA-ROU and DHN-ROU as you cannot remove a train from the intermediate stations between them. So if any one among these is to be rerouted it has to be between ROU and ALLP and one will follow this same route again because of the same reason. In that case we have only option to go via G/NGP, and any one may be extended to Trivandrum/Kochuveli.