For the short term (2-3 years) the company can manage the expansion through various flexi schemes/summer contracts. After that my guess would be that it would have to start hiring DEPs to maintain experience levels. I have no doubt it is a fine line at the moment between the right mix of Cadets and experienced SFOs as far as Operation Risk assessment is concerned. We could find an increase in things such as unstable approaches/Go arounds etc which could start to increase the insurance premiums.
As for why so many were interviewed and placed in the pool. The board has only just signed off on the revised fleet numbers; up to that point there was a very clear strategy of aggressive expansion hence the need for high numbers of candidates.
Good luck to those in the pool but I think you need to have a plan B.