When your company cancels your visa , all you have to do is show it to the landlord.
The landlord will not ask for the rest of the rent as you can prove you are leaving DOha.
This is the only time you can get out of a signed contract unless there is a clause in your rental agreement that says there is a notice period to pay for.
Give your landlord plenty of warning that you are leaving and then when your visa is canceled, show it to him, he should give you your cheques back.