I don't know if this is the right forum for this, but it can be moved if it is. If you sell a domain that has a high Page Rank and everyone deleted the links to that site, since its not the same anymore, or you delete all your submissions to directories and such, would that pagerank go down after a while?
Yes, you would lose all the page rank for sure. Unless you start pointing new links at it, but they would need to be of good value in order to maintain the 5.
As everyone already said, yes, PR would decrease. I had a website who used to have a high PR. The PR went down since I did not have the time to promote the site anymore and the backlink links got buried.
live pagerank will go down as soon as google notices but the results won't be seen on the toolbar for up to a few months or so; so you can have a domain that shows pr even though the live pagerank might be 0