Well, I'm not sure I'd use such absolute language. For one thing, people can still perform a 51% attack and try to influence decisions covertly, without triggering a split.
Also, the spectre of a 51% attack required for some major compromises to be made in the DAO design- Having a company that can arbitrarily split at any moment is likely to have a major impact on the future operations of the DAO.
In terms of the split, if the community broadly agrees that there is an attack, then I don't see it having a long-term detriment. However, as you said, if it is more 'stealthy' then it would be harder to detect and correct.
All that being said, I think there is a theoretical safety mechanism in place. Whether that will work in real life or not, we'll wait and see. I am sure some good lessons will come out of this in either case and the next generation of applications can improve upon some shortcomings.