Open Question: Joint Tenancy Agreement United Kingdom?

Ok so there are 5 of us sharing a house from the 1st of July for a year in a joint agreement and one of us has dropped out and moved home to another city (because he dropped out of university) We have tried and not been very successful to find another housemate and now are worried because we can't afford the cost of the rent between four of us? What happens come the first of July if we don't have another house mate? Legally where do we stand? I don't want to wait until the first of July for him to turn around and kick us out we do have a £200 Deposit but that's not a be all and end all Any help really appreciated