You won't be able to advertise uni-owned accommodation outside the uni, so not Gumtree etc. Your uni should be able to advise on their internal process for what you want. There may be a waiting list for your accommodation, from which they can find someone to take over your room. Failing that, they will give you pointers on how you might go about finding a new tenant.
Student Finance loan repayments are linked to how much you earn. You won't start repaying until you earn £21,000, at which point you will pay around £9 a month at the current rates. Repayment amounts will only increase if you start earning more. If you earn below £21,000, you won't make any repayments at all. I started uni in 2008 and I made my first repayment last month! Seriously - at this stage it's much more important to justify the debt by concentrating on your studies, than worrying about a scenario which a) might not start for years and b) when it does, you will barely be impacted.
No degree will be "a black hole which engulfs your future". You are getting things very out of proportion and I'd advise you to go and talk to your uni's Student Support folks.