Second-violinist checking in here… In one of the orchestras in which I play, we’re about 4 rehearsals in, and the concertmaster has yet to decide bowings on most of the parts. I’ve done some of it myself, but I don’t intend to take on that much of his job. And yes, it isn’t well-organized at the moment.
Sorry… just venting here, since it came up. Since I’m not contributing anything else I’ll shut up now. 
Oh, that Mozart, what a siut he was. 
It’s not uncommon at all for soloists to break a string while performing. I’ve seen it happen several times in performances I’ve done. Seems to me that the concertmaster just made do with the soloist’s crippled instrument. I can’t recall ever seeing it passed to the back of the section. A good violin is worth hundreds of thousands of dollars, I don’t think a soloist would want it getting manhandled by the whole section. It happened once in a dress rehearsal with a particularly arrogant soloist, and after finishing the movement with the concertmaster’s violin, the soloist remarked, “How can you play this thing?” Personally, I thought it sounded better than the soloist’s instrument.
No, you’re right, unless it’s near the end of a movement, a soloist will stop outright and fix his fiddle, and begin the movement again. A soloist taking the leader’s violin is much rarer than the leader taking his deputy’s.
Continued thanks to everyone. I’ve been enjoying symphonies for years (luckily, my parents started taking my brother and me to the orchestra when we were kids), and it’s great to finally be learning some of this stuff. The CSO site mentioned in my OP and jayjay’s post has been quite educational, as well.
I’ll be seeing/hearing The Academy of St. Martin in the Fields in a couple weeks, and will keep my eye on the concertmaster’s instrument…just in case a string breaks or something. {grin} (The featured soloist is a pianist: if he breaks a string, I think there will be some real trouble… )