Hi all-new poster here so hope I've got the right place.
I work in quite a specific field, and have been covering some of my managers tasks whilst she is on maternity leave. Due to nature of work, all of jobs are fixed term (or so i thought!).
I was told the "promotion" would only last for the length of the mat leave, and I would then return to my old role/level. This was said by my manager, who has previously tried to stop me going on training and development as it would be "over my head" (I have a degree and am undergoing further training). Before she left she seemed keen to give me the extra tasks, whilst not really specifing what they were/how things worked and providing minimal training. I spent the first month incredibly stressed and feeling like a failure, which was awful and became worse when i discovered two of my colleagues have had their fixed term roles made permanent. One is a good friend of hers, the other has been in post the same length of time as me.
I was not given the option of a perm contract, or change of title or even an update to my current contract to state my new responsibilities/pay adjustment. The latter is the part of this that makes me most 
I now wonder if this lack of training/formalisation was deliberate (we have not been given an interim manager which has made day to day life quite hard. None of us in the team have any management responsibility. We report to a mostly absent v high level director of division). Others have pointed out that perhaps leaving things in chaos would make her "missed" and her arrival back more welcomed/job more secure.
I don't have an issue with this lack of management during the mat leave, and i have come to terms with how i was treated in the beginning however I have made significant improvements to the running of the department, which have been recognised by our division director.
I am concerned at the end of the mat leave, that i will return to my old role with no scope for promotion. i don't want my manager's job, and i look forward to working with her again. However, how can i use the remaining time of the mat leave to shore up my case that i have improved the department operationally and levy my good working relationship with our director to allow for some form of progression in my role?
I've worked so hard for our department and it would crush me if i had to return to my role exactly as before. I want the best for the team, and feel i have really delivered this year to make this happen.
Do i discuss this with my manager which she is back (shortly)? I know i should, but i also worry her insecurities will encourage her to constrain my role. How can i broach the subject to make her see it's worth both our whiles? I like and respect her as a person so really don't want to make things uncomfortable or difficult.
Re the title of my post, am I flogging a dead horse in working in what will potentially become a "tight leash" environment/favourites etc again, do i look for something else?
Thank you if you read all the way to the end!