Are you asking if the landlord is able to do this?
Are you named on the AST?
Assured shorthold tenancy agreement?
in that case, I'm afraid that you are liable in your own name.
An AST renders you jointly and separately liable so either one of you could be pursued.
Of course, it is open to the landlord to exercise discretion in your favour but he cannot be compelled to do so.
He is already doing more than he has to strictly by allowing you to leave as long as you are replaced by new tenants.
I'm very sorry and I know that this is a personal tragedy but I'm afraid that your misfortunes can't be visited upon the landlord.
Can I clarify anything for you?