Whoa, this is what I have been wondering for some time, for my crawler.

Crawler results depend on domain authority. If page owner, or page contents page change the ranking may, or should change.

However original author also could change contents, and page ranking should not be changed. So this is not easy to determine what to do with domain of it becomes inactive, or changes contents dramatically.

Currently I use only 30 day window to keep track of domains. After that period inactive domain is thrown out of the window.

However valuable domains, even if dead, reside longer. My UI provides easy link to wayback machine. So even for dead links I can browse them.

I noticed also that some domains, even if expired do serve contents, even if author left it alone. Page contents is served, but with a text that it expired.