I don't know the answer to all your questions, but one thing you can do is sell it to a junkyard for the parts. You can call around to see who will give you the best price. You sign the title over to them.
Whether you can trade it in is something you'd want to ask a dealer. I'd imagine you won't get that much for it in trade-in value.
You could also try posting it on Craigslist as for sale, with the info re: the transmission. Someone who is able to fix it might purchase it.