Well If you have the 5-6ft tall variety of Calla lily then You must trade with me :) ... just kidding but would love to have one that big.

I am also in the seattle area and Mine,though smaller, do the same thing. They fall over right about now and look kind of scragly. But, the fact that they dont brown up and shrivel off tells me that they are still doing their job and feeding the plant. Maybe if you can stake them up or tie them up in a way that they can still do their job. My fear of cutting mine down is that the bulbs will eventualy get smaller and smaller because they wont be able to get a full season in with their leaves functioning. maybe some Calla experts will chime in..
Ps if you would like to trade.. I do have a good number of interesting things..

Chris