Exactly which version of Photostory do you have? This should not make any difference but it would be helpful to know.
The "loss" of the preview/monitor screen is not one I've ever heard of before! Are you saying that if you open PS in Timeline View you don't see the following:
with the proview screen clearly in the top left corner? If not, can you post a similar screenshot of what you actually do see?
In other Magix programs there is the facility to reset to the default Windows layout, often by pressing f9, but I don't see that option in PS.
I have got it back by reset program to original settings. Does not make sense because I not changed any settings. Did change view to tile view to change photo sequences. It vanished when I went back to the normal view.