Well, it's "towable" - you towed it home (yea, I know, but not realistically safe to tow). Anything can be repaired! Depends on how far you want to go with it. Someone will buy it - but probably not for want you want to sell it for.
"Nothing left to do but relinquish it back to lender." - So... are you planning on relinquishing it? or is that just an option? Why were you looking to sell it? If you have to spend the money to repair it, definitely look into keeping it and use it for a few more years.
You have options.