There's really no reason for DVC to start worring about the ending date until at least 2012 - which puts them at a 30 year lease point.
When you consider that most of the industry (as far as I've read) is typically only selling 20 to 30 year leases, the time allowed with DVC is still quite generous and will stay that way for a few more years. Shucks, I've even seen people voice as concerns about purchase that 2042 is too long a time period.