Volkswagen Passat 2003

my car overheated and i need a new heater hose because of a leak. they ran a combustion check and it failed. they said i need a new engine or i need to replace the gasket on top and hope there are no further cracks. She said that fluid and oil are mixing together and if i try to drive the car the engine will lock up. is this true? The mechanic told me i could buy bluedevil and it will probably fix it for a couple of months, which will at least buy me some time. Is there any way i could just replace the hose and not the engine or will the car not run? I have a Volkswagen 2003 Passat