If that happened, then I don't think Bronson Arroyo would be the answer to that. You'd need divine intervention to stop that downfall. But, just for the sake of argument, let's say that we are hit with injuries to that amount.
The Red Sox have plenty of viable options who make much less, and have equal or more upside then Arroyo. Jonathan Papelbon, could easily step in and be a very good starting pitcher. Lenny Dinardo, could equal Arroyo's numbers as a starter. Jon Lester whom could be ready by July, has way higher upside then Arroyo.
It's not often, you're offered outfielders with 35 HR power potential for a fifth starter. Even if Pena never improves his OBP skills, he's still a great fourth outfielder, who mashes lefties.
What happened was a f***ing miracle, and I want you to acknowledge it.