I'm not a pro, but in my limited expierience length was just a small factor in breaking the bows I did and an unseen hinge or a cut across the rings on the back is substansially more lethal to a bow.
Length will effect how much stress is on the bow, which will effect string follow, but even in some extreme cases I've seen in really short bow, length alone (within reason), isn't enough to break a bow. Proper tiller and a clean back are much more important.
That being said, longer bows will handle stress better, and there's a bunch of other things they can do but that assumes proper tiller and design, not just length.
Any pics of this osage bow?