Why would you decide to drive for a month with an empty coolant bottle?
Why are you keeping your options open as you suspect bigger problems,it's a diesel focus with a blown head gasket.
Why are you worrying about it,keep topping it up if you don't think it's a problem and stop coming on here asking questions every 5 minutes.
This is not a diesel focus forum where everybody's a mechanic and expert on the marque,the folk that have tried to help are being ignored so either get it fixed by someone who knows what they are doing or drive it until it stops.