You can check the terms and conditions of your warranty for the detail on what is and is not included, but in the case of most warranties the air conditioning gas is considered a consumable, in that it eventually will run out. The same applies to things such as tyres and brake pads, as they have a finite life in the course of normal use. If it is the case that the gas has escaped because of a component failure or manufacturing fault with the system then this is potentially a different matter, but if there is no fault then we not expect regassing to be covered under warranty.