When the Viper was introduced it was a 'halo' car: something to make people think Chrysler had products worth examining. Let's not forget that this was still the era of the dreaded "K-car". Part of the engineering justification was learning how to work with composites that led to the minivans.
So it's now 15 years since the designers went to work on the Viper and things have changed a lot. DC no longer needs a halo car: the product line includes gorgeous cars like the Crossfire, Charger, PT Cruiser, Magnum and more. An engineering justification? Probably not: the smart companies are investing in engine technology and better manufacturing neither of which a hand-made gas guzzler help with.
Can the Viper survive on it's economic merits? Maybe. I don't really know what the margins are like, but I know that there are a *ton* of supercars now in the $100-150K range. You've got everything from gentleman exotic touring cars like Aston-Martin, Panoz, and even DC's own cars. On the performance side the market is just silly with cars from Porsche, Lotus, Ford GT, Ferrari, and TVR (in non-US markets). Can the product be positioned a little less expensively? That doesn't seem too likely either since the Corvette has an incredible price point. (I can't stand to own one, but I have to respect the price/performance package.) So you can't go upsteam (over $100K) and you can't build a car that is less powerful than a Z06. That's a narrow range in which to design and market a car!
The good news for DC is that the Viper has enough of a following that many still aspire to own one. There is a market of guys who want great performance but can't stand to consider a Vette. Moving upstream probably can't work, but keeping the car around $80K should result in sales.
One thing I don't think that affects the car is the price of gasoline. People might drive them less, but the truth is that not too many people use their Viper as their daily driver. They want an exotic that they play with from time to time. High fuel prices stunt sales of SUVs and V-8s like the Magnum and Mustang (note how the great styling on both those cars has helped them). If anything, it makes an exotic even more exotic and thus more desirable.
Should be interesting to see what DC comes up with. The car certainly could be cancelled. It might also be able to be farmed out to a speciality shop much like Ford did with some cars. 2007 will be very interesting!