I am newbie here. It's a sad story.
But I just didn't get it, maybe I am wrong. If you have a 100/110/120 iron fly. Then you have a 110/120 call credit spread in it. With the short 110 call be assigned, yes you will carry huge borrowing cost. But remember you have same amount of long 120 call, you can immediately ask broker to assign that part of the long call, to offset the shorted stock. That shall make the book even, with no additional loss.
Am i missed anything there?