I don't think Josie has anything to worry about. I highly doubt John is going to do a massive exclusive now, there just won't be the interest and really if he has done what people assume and gone back to his old life then its hardly controversial enough to make magazines.
Even if John does come out with an interview Josie has reached a point now where is shouldn't affect her. She seems to have completed quite a few of her own goals establishing the beginning of her presenting career, losing weight and looking fantastic, and doing things for herself like the balloon flight. I'm not sure what 'dirt' John could have on her now to get to her.
If its an article about Sherrie - Josie knows about her. She has done for months now, its not going to be a shock and Josie would probably have a heads up anyway so she should be prepared before it hits the shelves.
If it is just a case of John coming back to London to promote modelling etc - well he has every right to be here and make a career if there is interest. That is something Josie will have to accept. I quite like the idea of them both being in London...Josie on BB, John a big BB fan is bound to watch and see her present. I like to think they will be closer to each other.