A well informed Land Rover exec told me at the Range Rover 4.4 TDV8 launch in Australia (item below) that the company believes it can keep the current Defender in production until 2015. The Defender's demise has been predicted many times, including by 4wdNewz, but it just seems to be able to soldier on. He said inability to re-engineer the vehicle for airbags will cause its demise. Whenever the "old" Defender goes, it's likely to be replaced by a new one on a version of the Discovery chassis. Or not. The old truck has an uncanny ability to defy predictions!
Here's more on the topic.