Having browsed through the "top 50" user profiles, I noted that quite a few of them haven't visited the website in a while, some even in years.
Whilst it's understandable that many people change their interests over time and some just naturally move on due to time constraints, etc, it would still be valuable for the site if some of these high-rep users made even an occasional contribution sometimes.
Can we think of any ways that some of these users could be brought back to at least semi-active participation?
Here are some of my own thoughts, please share yours if you can think of any, and perhaps some of these could then be implemented?
Reminder email once per 6-months (or once per year), along the lines of: "We miss your contribution, and would love to see you back on Quant SE. Here are the 5 highest rated questions and 5 highest rated answers over the past year whilst you've been gone" (perhaps at least the user would be interested in clicking on the linked questions & answers, and this could bring some interest back. Of course, the user could unsubscribe...)
Some sort of badge: I know there is the silver yearling badge if you're active with at least 200 rep. But what about something like a badge return-of-the-hero, if someone with rep > 5K (or something similar) goes inactive for a year and then comes back and makes a contribution >1K ?