A solo violin will eventually have to change bow (turn the bow to the other direction). Some great violinists have been known to do that so well, so as the public could not tell when it actually happened. But it's there alright and there's nothing wrong in asking for that.
For a violin section, however, things can be a little different. If you have 10 violins, for example (or 18 for that matter), and each one change bow at a different time, it goes completely unnoticeable, and thus one could assume you get an indefinite... legato (or tenuto). Same goes for a choir. A human must breath, but a choir can breath unsyncronized, thus retaining the sense of continuity.
Moreover, for the strings there are other techniques which will allow the violin to play longer sustained notes, sort of... For example the tremolo (tremoli in plural). You don't get long bows, but very short ones, so you can sustain that for as long as you want (of course it becomes tiring if you over do it).
The 5th Symphony by Beethoven, has a long sustained note after the first three notes. If you're referring to that, I believe that it can be done with a single bow, assuming everything else is a different bow, or a detached bow.