Joint Tenants splitting up.

Access

I have an AST with a couple who have a 1yo baby, which has been running since Nov 1st 2010, and expires on 31st Oct 2011. Both their names are on the AST. They are on benefits, and he was her carer as she has mental issues. The rent was agreed as matching their allowed LHA of £257/wk.
He has now informed me that they have split up and she and the baby have left the property to go and live with family. He has enquired about his LHA, and by all accounts his entitlement is £219/wk. He will now go on jobseekers allowance until he finds a job.

I would like to know if i can continue with the current AST with the male tenant as a single person, and whether the council will have any problems with the situation? I believe whatever arrangement i have with the tenant with regards making up any shortfall, would not be of interest to the council.
Also, do i have to have any written notification from the female tenant?
And what problems can i expect if he gets a job, with regards his LHA etc?

Are there any other scenarios i need to be aware of in this situation?

regards

Changnoy