Why is anyone holding this stock at 20PE? Pretty outrageous valuation for a company with declining revenues. I wouldn't figure earnings to keep coming in if sales are down.
If you had to be in this space, Papa Johns is trading at the same earning multiple and actually has solid sales growth (perhaps taking business from Dominos as it has for years. Heck, you can buy McD at a 16PE and much stronger fundamentals and a 3% dividend.
Ask yourself if you would buy the local Dominos in your town that has flat sales for a 20x earnings. Maybe 3-4x is what you might offer so why pay more for DPZ?