If this is true it could be a double edged sword.
Advantages are that MAG seem not to know what to do or how to handle this size of airport and have probably been responsible for some of the losses at BOH in recent times. BOH seems to have all but dropped off MAG's radar in terms of new route development. Rigby group will hopefully be able to focus a little more and start to compete more effectively for business. Not sure if the site would also include the aviation park which is quite profitable to MAG.
Negatives are that Rigby group will not be able to afford anything like the economies of scale that MAG was able to offer so further investment in the airport will most-likely stop. They are also working with some of the smallest and most niche type airports in the UK including Norwich and Exeter - neither of which are Ryanair customers. I doubt that one of the 'richest men in england' will know how to deal with o'leary and his demands.