how does SF work when you leave?

I started my masters in September. my student finance was delayed because of issues with enrolling. I got into debt with my main bills (rent and council tax) so when student finance eventualy was paid, i paid off my arrears and was able to stay afloat. I'm now in the midst of a mental breakdown and I'm struggling AF to even get out of bed nevermind get to uni so I have emailed to withdraw/defer (still waiting for a reply). I know il have to pay some back regardless but il be unemployed living on what little money i have coming (altho i am looking for a job, not sure how il manage but i cant afford to be ill right now). If i set up a payment plan, will they accept this? I dont have the money to be able to pay everything back because iv used it to pay my arrears off etc. Id be grateful for any advice.