IMHO the thermos is unsaveable if coffee was left in it . . .
Coffee just doesn't come out of any thermos, or at least not with all the methods I have tried. It comes off the glass or steel thermos liner, but if the coffee has been in contact with any plastic of any sort, you will never get the coffee flavor/smell out. The thermos is still usable, but use it for coffee or hot chocolate or other things you don't mind the aroma/flavor of coffee mixed into.
I keep a thermos for coffee and a separate thermos for other stuff like hot tea.