That will encourage continual good behavior.
Of course, the reason to avoid putting dead players in the rankings is that the people who prefer watching competitions between living players -- i.e. the majority of fans -- don't want the dead ones cluttering up their leaderboard. But this is the web, not TV, so the solution is simple: Multiple leaderboards. Create a version of the HN leaderboard that only counts the past 52 weeks. Put it up at some URL or other. Then people can decide to use the alternative leaderboard if they want.
Heck, if we want, we can allow every reader to create his or her own leaderboard algorithm. Then we can have big chair-throwing debates about which leaderboard best represents the True State of Play on HN. That is exactly how the world of baseball statistics works. ;)
It's also slightly more difficult because what constitutes good behavior isn't always black and white and isn't even always agreed upon.
If that's what you're gunning for, it's a great idea. What's popular is only dependent on your users and their tastes, and this can change over time.
Tennis rankings are based on physical form. Physical form is something much more likely to change year to year than intellectual form.
Someone might be out of date with the latest topics, consensus from the community, etc but it doesn't imply their thinking apparatus or world view has dramatically altered.