The clematis needs reviving. Wait until February/March and then go to work on it. Cut it back (every stem) to a height of about 12". Apply Epsom Salts (1 tablespoon to a gallon of lukewarm water), add some manure and compost around the base. Any stems that are old can be cut back but may just break off - not a problem at all.
I've often cut it back in the fall, so if yours is too unruly you can cut it back now and again in February/March.
You could try and divide it but that's not a quick or easy job.
It's worth a try to unearth the two canes you spoke about. You have nothing to lose.
Jackmanii grows so lush and full that I don't count stems left or stems remaining. When a stem shows buds you know it's alive. You can cut other doubtful stems right down to ground level.
