To be honest I was never in a position where city was bankrupt, as I financed it from the start.
Other option would be to simply purchase city's land or resources so it could finance media firm or whatever is needed.Once town has media company it is easy to pump the money.
Also I moved a lot of production to my city to achieve triple benefit.City earns from taxes, and selling land and natural resources.
Also i limit available tiles, so only city can build apartments and commercial buildings.
What I do is, when the city is bankrupt, stop the time.
Then, go to the city government mode and put a commercial building or apartment on sale. Or media firm on sale. Then my company buys the buildings, and if you have tons of money, you can manage to pay the city millions or even billions of dollars when you buy these buildings - and boila, your city got money.