I wouldn't try to save the batch as bread. Really, if it is completely overproofed, the yeast is spent and you can't get good leavening any more.
This doesn't mean that you should throw it out. If it is overproofed, chances are that it spent a long time leavening. In this case, you got some great gluten formation. In case you used a good (=low) amount of yeast, you also got some great fermentation taste*.
So the best you can do is to use the overproofed dough as a preferment. Make a second batch of the same proportions, and mix the old dough (cut in pieces) into it. Do it at the beginning of the mixing process, the way you would do it with a biga. Then proceed with the new, double batch as usual. You will have better gluten and more taste than if you used no preferment.
*There is a caveat here. If the overproofing is due to too quick a fermentation (which seems to be the case), then the tastes produced will not be as pleasant as if it were a slow-but-too-long fermentation. It can be that using the preferment in this case actually makes the taste of your dough a bit worse, rather than better, in relative terms (as compared to no-preferment). Still, you have good incentives to use it if the absolute taste is good enough for your palate: you don't waste the materials and the time you invested, and you get a better texture due to the good quality gluten in the preferment. But if you think that your fermentation was too quick, reduce the amount of yeast in the new mixture.