Agree with the emergency scenario. It will always be beneficial to have BG locos ready to operate on the track in case of emergencies.
Center of gravity and capacity are not really a problem. Standard gauge is barely 20cm narrower than broad gauge. There won't be any effect on carrying capacity as pretty much the same coach shells can be used for both gauges, just on different bogies. Center of gravity is also more of a design parameter and not really dependent on the gauge. Many American locomotives and rolling stock are heavier and taller than their Indian counterparts and run at higher speeds on Standard gauge. For light-axle load train sets, ride quality will be...
more... identical between both, with SG being slightly cheaper.
Standard gauge was never widely used in India. They were mostly used around ports and on tramways but there were no long routes. All of them were converted to metre or broad gauge to avoid trans-shipments and additional equipment. I am not sure about a history of failures. It will be useful if you can share any information about the same.
Since most of the high speed rail is on standard gauge, it would be a very cheap alternative for us. There isn't much scope of BG high speed railway anywhere else in the world, so developing a BG high speed train set would be a herculean R&D effort, and will take several years to complete. Using SG would let us use any of the numerous existing HSR technologies already implemented elsewhere.