Ford will be fine. The sales of the current generation Mustang may be slumping because of its body design, but it has several very well designed engines and a lineup of cars that in my opinion is the best looking lineup of any of the detroit 3. Ford can pull off a successful redesign. You can see it in their lineup. They just need to get it right for the next Mustang.
The Camaro is hot right now, but if GM doesn't offer as many options as Ford does in regards to accessories, options such as gears, navigation and even models (v6, gt, boss, gt500), the Camaro's sales will eventually slump. We are just lucky that most people consider the Camaro a better looking car today. Ford has been refining the Mustang since its inception. The Camaro is now a totally new design, it kicks butt, but don't be fooled. Ford isn't happy with being number #2, especially when the Mustang was the ONLY pony car to enjoy uninterrupted production.