To be honest, the system should be self governing in the way that stadiums are reduced. If you drop down your stadium shouldn't automatically become smaller, and you shouldn't really lose the money you already earned.
Stadiums should all have maintenance costs that have to be paid each season. The maintenance cost would be tied closely to the size of the stadium. If you can't afford to maintain a certain section of your stadium, it should be removed. When teams drop down, they should have their fan support tanked (would you still love your favorite NFL team if they started playing arena football or in some mexican league?), resulting in much less income, which would mean they couldn't maintain their stadium.
Of course, this would require a complete overhaul of the financial system. We can't exactly be spending money maintaining our stadiums when a pair of cleats cost $3,000,000.
Stadiums should all have maintenance costs that have to be paid each season. The maintenance cost would be tied closely to the size of the stadium. If you can't afford to maintain a certain section of your stadium, it should be removed. When teams drop down, they should have their fan support tanked (would you still love your favorite NFL team if they started playing arena football or in some mexican league?), resulting in much less income, which would mean they couldn't maintain their stadium.
Of course, this would require a complete overhaul of the financial system. We can't exactly be spending money maintaining our stadiums when a pair of cleats cost $3,000,000.