So, I called a couple of the people I know here in Boston, and my friend Karen came over to help me contemplate the sofa situation. "If nothing else," I told her, "bring some objectivity, because I think I've lost all sense of that with this situation." She arrived just as I was contemplating whether I would be able to get it successfully reupholstered if I just sawed it into thirds and moved it up that way.
Turns out, it looks like you should be able to detach the sofa legs (although, it is not certain that removing said legs will solve the problem). The sofa legs are held on by 10 really long screws. Karen and I were able to get 5 of them out, and then decided we needed to go to a hardware store and get some WD40. This helped us get 2 more. So 3 screws left, which we can't get to turn and fear that we are on/past the verge of totally stripping the screws. So, what now? Seriously, I'm calling on the blogosphere for help: if anybody who is handy with these sorts of things has any ideas about how I should proceed, let me know! I don't want to sound desperate here, but I am, in fact, desperate here.