Joint Tenants w/guarantor moved out early . Owe rent and making offer to pay installments

Rent Arrears

Let flat to a couple in Oct 08 who paid 1st month's rent but no rent in Nov or Dec. They had series of very convincing excuses for delay and were receiving housing benefit for rent (this was first time they'd had it paid direct to them). I kept guarantor informed of delays and kept close contact with tenants.

I was due to collect rent payment last week and told them wasn't accepting any more excuses. Half hour before meeting received text saying they'd moved out to stop debt increasing (they left keys in flat).

Have spoken to them since and advised them they have 6 months contract so liable until flat re let. Following family pressue they have made offer of £60 per month but not convinced they will pay. Have now found out kitchen flooded where they unhooked washing machine.

Questions: Do I have to accept their £60 a month offer? (would idealy prefer guarantor pays me and they pay the installments to guarantor) - they owe about £500 assuming I get deposit back from custodial scheme - (about £1100 if not) If flat doesn't rent it goes up by £500 a month.

Are they responsible for the water damage? Don't know if it occured while they were in flat. Think more likely it was the hoses leaking when they disconnected washing machine and it has warped kitchen flooring.