Someone came over for dinner about two weeks ago, and brought a very large bottle of very cheap champagne. We had a few glasses, then I used a bottle stopper kit that I had received as a gift to re-stop it. Last week, I noticed the bottle was leaking and put a glass underneath it. Now I have a very large, leaky bottle of cheap, and now probably very flat, champagne. Is there anything at all I could use this for, or should I just dump it?
If it was not very good to begin with, it is not going to be any better now. Just pour it out.
You can make vinegar. I do that with all of my leftover wine. But it's probably not worth the investment of time and equipment unless you're willing to keep it up as an ongoing hobby.
Is the wine at least methode champagnoise? That is, do you know if it was actually produced using the traditional Champagne method of fermenting in the bottle? If it's not, I would just toss it as the stuff made using other methods can give you nasty nasty headaches.