Unless you've got a spare pedal from the same series that just so happens to be dead... it might seem the only choice is to swap out the switch for a large momentary stomp switch to maintain the FET switching or a 3PDT for true bypass. Not everyone wants their pedal to look different though...
I had a guy come to me today with a dead switch on his 808. After testing for continuity when actuated (fail), I took that proprietary switch apart. Lo and behold, there's a tiny little surface mount momentary in there. I'd never seen a switch so small in my life! It was so tiny, in fact, that I could even tell if anything was moving down when I pressed it. I could search Mouser for days to find a suitable replacement, so headed down to Radio Shack on a whime to see if they might have something small enough to squeeze in there... AND THEY DID!
http://www.radioshack.com/product/index.jsp?productId=3020763It was a touch bigger than the original, but I bent the legs a little and glued it into place before I soldered the connections. It worked like a charm! I had to remove the spring that normally bridges the gap between the physical button and the momentary, but since the button is spring loaded to return to the up position, it was no problem at all.
I hope this helps someone. I know when I first went searching for info on the TS-808 switch, I couldn't find anything!