They were delicious, but there's still a good dozen left. Can I save them? Also, what about the ones I didn't cook because I thought were dead, but they finally revived. Do I just toss those in the regular trash?
If the supposedly dead mussels are really alive, cook them up right away and add them to the rest of your leftovers.
A dozen leftovers won't go far, but you can keep them for a couple days, adding them to salads or just eating them up when you'd like a little snack. Mussels are remarkably, somewhat surprisingly good, in pumpkin (squash) soups. My brother often cooks a lot of additional mussels, puts them on skewers, brushes them with olive oil, and very briefly grills them over charcoal. They come out smoky and delicious.
When I was in the seafood business and we had mussels leftover from the weekend, I would bring them home, steam them briefly, and freeze them in their liquid. Next time I made chowder, I'd add them at the end. I've actually seen frozen mussel meat in stores.
You could do a small batch of one of my favorite mussel dishes - cold, on the half shell, with a classic Ravigote Sauce (a bit retro French and really delicious.) I kind of eyeball it, but this online recipe looks pretty close - varying the herbs, etc. (I'm sure Julia Child, Jacques Pepin, Pierre Franey, etc. have versions of the recipe too):
Just start from the point where the mussels are already cooked. A great first course, or by itself with a glass of cold dry white wine. Yum.
Forgot something - you could reduce the quantities to just make Ravigote sauce for 12 mussels; but it's also delicious on cold shrimp, poached salmon, etc. - so any add'l sauce need not go to waste.