I don't think your co-founder really stands much of a chance honestly, except he/she can hold any money etc that you put into the company. So honestly, it might be worth an hour of time with a competent attorney to ask a few questions and make sure you do things to insulate yourself.
That all said, I can't imagine what they would sue you over in this case for not signing. They are literally on the other side of the world, and unless your co-founder is just flush with cash and an ass that is willing to tie up your time in court etc then I doubt this amounts to anything other than hurt feelings and a shit relationship, at least for a while.
