Bread – Making Bread From Pizza Dough

I'd say your problem is that the yeast has exhausted the food in the dough before you even get the leftover dough in the fridge. When you pull it out the next morning, the yeast does nothing or very little because there are no more sugars left for it to eat. And not only will this prevent rising, it will also limit browning because it's at least partly the sugars that brown in the oven.

You could work some more flour (and water, to maintain hydration) into your dough as yeast food--maybe even a little sugar if you want--and then rise/form/rise and bake. But at that point you're doing what @tmow suggests--just using your pizza dough as a starter for new bread.

Normally, you would not be doing a final proof overnight—that is, the proof that you have done to form the loaf. Instead, you would do the first ferment or proof overnight, then form the loaf, let it have its final proof, and then bake it.

The dough won't be wasted, but you don't want to bake a formed loaf that has over-proofed and fallen. This is because the gluten network will have collapsed and you will have a very poor structure and strange texture. You will need to reknead the dough, form the loaf, and reproof it:

Per The Fresh Loaf, you can almost certainly just punch the dough down, and let it proof again. It may actually have an improved flavor.

Cook's Illustrated concurs:

Using your fingertips, gently punch down the over-proofed dough and reshape it into a ball, then allow it to proof again for the recommended amount of time although it warns your final loaf may be about 20% smaller.