We can subscribe to The Quora Memorial, and post our memories of the deceased as comments there. That’s a start.
Dion Shaw’s answer of commemorative blogs is an excellent suggestion.
And in your own content, continue to echo them. Link to their answers, praise their insights, keep their presence on the site evergreen. Don’t expect the site to do so for us.
Do so, not for those who have passed. Do so, for us. Because we do care, when one of our number is no longer among us.