Perhaps the new owners would regard existing Flybe senior management with a level of suspicion - quite reasonable given the financial mess - and want to ensure that the CEO is someone who the new owners know and trust ?
Flybe is in a bad way - and major changes to reshape the airline will be coming which needs someone with strong experience from a profitable aviation company and also to be seen as capable of being ruthless against an entrenched old guard. Putting fear of job losses into the hearts of existing staff may encourage people to raise their game a little
My guess is that some of the existing board of directors or senior management at Flybe may be shown the door fairly soon as part of a general shake-up - I think Saad did a clear-out shortly after he joined