The reason they are replacing Halley V is that there is an increasing risk of the ice shelf breaking off after 2010, taking the site of the current base with it. Not only will Halley VI be built further inland but it is being designed to be movable so that it can relocate if it is in danger of breaking off.
If it wasn't for the risk of carving, the current station certainly could survive in its present form for a number of years. The only serious problem with Halley V is that the sub-surface tunnels that contain the fuel stores and services between the buildings are getting very deep and increasingly crushed by ice. If they abandoned the old tunnel system and started on the surface again I don't see why the base couldn't continue for another 10 years.