Saw this Twitter status update:
Does the #bitcoin protocol have a version number that allows to upgrade if someone leaves the system for 5 - 10 years? http://twitter.com/stephanwehner/statuses/16224034316361728
I think what is being asked is, if a client were not upgraded for a very long time, could it still communicate?
Either way, will the future clients be backward compatible as far as being able to access today's wallet.dat?
A lot can happen in 5 to 10 years.
IPv6, various vulnerabilities discovered, encrypted wallet.dat, etc.
(Incidentally, ... isn't the reason most who have left the system for 5 - 10 years due to being incarcerated?)