from what i have heard, people go to bangalore, and then onwards to chennai. while it wouldb't be very comfortable, it would still take less time, or atleast equal time (mumbai bangalore takes around 18 hours in bus, Bangalore chennai is bound to take 6 or less than that) than 12163.
Thing is, south-west connectivity is horrid; lack of any heavily biased RM from this region means that railways never bothered to run half decent trains between the major destinations in this section, unlike others where mumbai/bangalore/chennai each have excellent SF's to many parts of country