In my rebel simulation I had WB'd a city as the 'rebel base' and moved units from there into India. As per the scenario if the rebels managed to get a victorious battle other cities would flip and then using the enlarged army the rebels would take the former capital. After the rebels won, India wasn't collapsing because at the end you controlled enough of your core provinces.
I honestly thought that's how you played the different scenarios. Considering that it was our plan to flip the army at the two other Catholic cities it would have been easy to take out the rest of Ethiopia. Yeha had iron and massive production, its in fact one of the most productive zones in the map. In 15 turns we could have out produced the enemy and taken the capital with our starting forces + the flipped garrisons.