RNCM Reserve Offer - how likely will it be converted?

Hi everyone! I am a 30 year old soprano and have never been to a Conservatoire before, but auditioned for RNCM and RBC last year and received two offers. I have a guaranteed offer to the PGDip course at RBC, and received a Reserve Offer for the Advanced PGDip course at RNCM.
I have made RNCM my first choice as I already have a teacher there and live in Manchester, so it would mean I could continue my current job part time and wouldn't have to uproot.
What I am wondering is how likely it is that my offer will be converted to a guaranteed? As I have no experience of being at a Conservatoire before I have no clue how likely it is, and as I work full time, rent my own place etc I am anxious about not having a clear plan of where I will be going in September.
Any advice anyone can give me will be most appreciated