Tenants breaking contract and leaving the country what can I do??

Rent Arrears

Hi I have a 12 month AST with no break clause and a clause stating my expenses for recovery of enforcing the agreement will be met by the tenants.

They gave me one months notice and wish to vacat the property not paying 3 months rent and want their depsoit back. The agreement in in black and white stating they have broken their agreement I know I am in full rights to hold their depsoit but my question is :

What can I do to get them to pay out the remaining rent they are obligd to do if they are moving to canada?

I know they are squeaky clean tenants who do not wnat any bad credit can.

I was going to send a solicitors letter stating my terms to pay 2 months more rent and for me to keep deposit ( letting them of 2 months rent) and that I will fiel for ccj)

will this have any effect whilst they have left?

please advise