The truth, whatever it may be, and what they feel the appropriate reaction should be; short-term and long-term. If there is nothing new or out of line, they should say so. If they have reached a tipping point that will require adapting, they should be honest. It's the last thing that occurs to most people, organizations or companies, but surprisingly useful, IMO.
1) Can the number be trusted?
2) Whatever the 'real' number, it is less how many than who is leaving. If a very small percentage of key people leave an organization, that could easily be enough for small, controllable issues to spin out of control. The Pareto Principal (80 - 20 rule).
3) Is a spiral effect a legitimate concern if the small percentage is an influential group with legitimate issues? If there is a problem and 'Deny, Deny, Deny' is the response the number could move in a hurry. They exist as the result of free effort, work, and content. Those people and their work could find other places to go right quick.