This is probably just hypothetical as it appears Bradley will recover just fine from the collarbone injury. However say if it were the playoffs and a crucial game, and Bradley had to miss a game or 2 who would you want to start? My guess is most people would pick Lee or Terry but I wouldn't be surprised if there were a few voting for Williams or Crawford.
I'll start it off and say Lee. His defensive energy is most similar to Bradley out of the group IMO, and I think he can handle the ball just fine. His size could be almost as disruptive guarding point guards. Whoever it would be I'm guessing would share ball handling responsibilities with Green and Pierce anyway. You take out that first month of the season for Lee, and he has been shooting very well from the field and from 3 point range. Never really spectacular but consistent.
I personally like Terry's O off the bench, and I really don't want him guarding opposing starting PGs that much. Crawford is too hit or miss with me, even though his offense can be explosive at times. Williams is probably the most natural PG out of this group but it would be way too much to ask of a guy recently signed.
I hope we never get to this, but with how hard Bradley plays you never know.