What do you mean buy "Viper". Do you mean the brand? Or the vehicle trademark? Or what? Viper is one of the products of a big manufacturer. You can't just "buy" the one vehicle without the rest of the engineers, manufacturing support, plant, marketing, finance, marketing, etc. Are you talking about starting a whole new company just to build Vipers???
It's a very simplisitic question to a very complex situation. If one buys the name brand of Viper from Cerberus/Chrysler I guarantee you by the time a private company comes out with an actual vehicle it will look nothing like, drive nothing like, or be as reliable as the Viper built by Chrysler. It will probably turn out like a kit car like the Cobra replicas.