Wasn't part of the original SA lock-up was that Leaders could not boot?
I'd go search the forum, but I really don't think it was much of an issue or many would have posted about it. I didn't see any posts about members getting locked out of their syndicates due to SA popping up without more notice.
There's really no reason to not be in your home syndicate, unless it's to help another syndicate with donations. It's a nice thing to do, but don't do it around the time events begin and you won't have to worry about it.
Edit: I had to look if syn's were locked for SA & how. This is what I found...
^^from http://forums.gree.net/showthread.ph...Street+Assault on 02.25.15
I guess they are totally locked like they are for wars.